300+ years after the fact seems like a long time considering the US is 247 years old. It's hard to think of people born after 2076 as being early fathers of the United States.
Some people impose an artificial distinction between “Ante-Nicene Fathers” and “Post-Nicene Fathers”, but to me this is problematic, because you have important Patristic figures such as St. Alexander of Alexandria, who was Pope of the Church of Alexandria during the council, who had deposed Arius, the event which triggered the council, and his protodeacon St. Athanasius, who would succeed him when he reposed as Pope of Alexandria, who basically prosecuted Arius at the council on St. Alexander’s behalf, and Arius himself, as well as various other bishops such as St. Nicholas of Myra, who was tortured during the Diocletian Persecution, and Eusebius of Caesarea, who equivocated and was at a minimum sympathetic to the Arian position, and was possibly an Arian, certainly, the only advocate of Arianism who attended the entire council (most pro-Arians like Eusebius of Nicomedia avoided the council and kept their cards close to their chest, as it were).
Rather I think the only meaningful distinctions can be made on the basis of permanent schisms which still unfortunately endure into the present, starting with the Nestorian Schism, which alienated the Assyrians from the rest of the church for a time, and resulted in the Church of the East being briefly under Nestorian control, until its Christology was revised by Mar Babai the Great in the Sixth Century along Chalcedonian lines, but which continues to be the only church to venerate Nestorius, most everyone else considering him to be rather gross), the Chalcedonian Schism between the Oriental Orthodox and what would become the Roman Catholics and Protestants, since the Tome of Leo, the Bishop of Rome, who opposed the council being held, but since it was held, became the only Roman pontiff to intervene in a major way in an ecumenical council, submitting a document on Christology that, while more or less equivalent to that of St. Cyril the Great, differed from it in key terminology, which made those churches, particularly those which consisted largely of non-native speakers of Greek, namely the Copts (and Ethiopians), Armenians and Syrians, great consternation, and leading to a schism which fortunately is now being reconciled, and then the Great Schism in 1054 when the Roman Catholic Church excommunicated the Patriarch of Constantinople for refusing to concede certain doctrinal points, which were divergent from Patristic theology, being driven by the new Scholastic Theology as it is known in Roman Catholic circles, which emerged in Benedictine Monasteries such as the Cluniac Monasteries, and was associated with the likes of Anselm of Canterbury and Thomas Aquinas. Indeed Roman Catholics view the 8th century Syro-Byzantine theologian Saint John of Damascus as being the last Patristic figure.
The Eastern Orthodox disagree; there was never an equivalent in either Eastern Orthodox or Oriental Orthodox theology to Chalcedon. So with regards to both churches, aside from the minor doctrinal disagreement at Chalcedon, one could read the Exact Exposition of the Orthodox Faith by St. John of Damascus (also known as St. John Damascene, primarily in older Roman Catholic publications), and everything in it would still be applicable at present. Indeed given the existence of that work, I myself have questioned the need for subsequent and voluminous works of systematic theology, such as the Summa Theologica of St. Thomas Aquinas, or Calvin’s Institutes, or the particularly massive Church Dogmatics of Karl Barth. What is more, the ancient writings, such as those of St. Athanasius (On the Incarnation, the Life of Anthony, and his various letters and other works), the Cappadocians (principally St. Basil the Great, his brother St. Gregory of Nyssa, and his best friend St. Gregory the Theogian, also known as St. Gregory Nazianzus), St. John Chrysostom, St. Ambrose of Milan, St. Ephraim the Syrian, St. Irenaeus of Lyons, St. Cyril of Alexandria, St. Cyril of Jerusalem, St. John Cassian, St. Vincent of Lerins, St. Cyprian of Carthage, St. Ignatius of Antioch, St. Clement, St. Polycarp of Smyrna, St. Justin Martyr, St. DIonysius the Aeropagite, among others, with all of those who I have just enumerated predating the Chalcedonian Schism. And there are some important saints from after that schism we also read, on the Oriental Orthodox side, St. Severus of Antioch, who had a huge influence on Eastern Orthodox theology and Western theology as well, which can be felt as far away as Lutheranism and Anglicanism, although few people are aware of it, St. Philoxenus of Mabbug, St. Jacob of Sarugh, and on the Assyrian side, St. Isaac the Syrian, and on the Chalcedonian side, St. Maximos the Confessor, St. Photius, St. Gregory the Great, the most beloved Pope of Rome among the Eastern Orthodox (not counting Bishops of Rome before the mid sixth century, who did not style themselves as Papem, or Pope; between the third and sixth century, only the Bishops of Alexandria officially adopted the title of Papem, or Pope, which they retain to this day, although the Alexandrian Popes have never claimed Supremacy or Infallibility, but rather function like the Roman Popes did in the centuries before the Great Schism of the Eleventh Century, as Primus Inter Pares, the first among equals within their own ecclesiastically sovereign church (ecclesiastical sovereignity is called Autocephaly among the Orthodox, meaning “self-headed”, and it is guaranteed to the churches of Antioch, Alexandria and Jerusalem, as well as Rome, by Canons 6 and 7 of the Council of Nicaea, which have the effect of making it uncanonical for the Roman Church to demand submission to it from the Eastern churches, which is what actually happened in the eleventh century, and when this submission was refused, the Eastern Orthodox churches were excommunicated. The principle in question however had been established previously; when St. Victor (the Bishop of Rome responsible for ordering the translation of the the Greek New Testament, the Septuagint, and the liturgy Into Latin so that the majority of Romans could understand it, which is ironic, given that later on, for many centuries, the Roman Church insisted on using Latin even after it was no longer well-known or understood) attempted to issue a command to an Eastern church, if I recall, the Church of Corinth, St. Irenaeus of Lyons, who was a senior bishop in the Roman patriarchate, wrote him a letter in which he explained that St. Victor did not actually have the power to do that.
At any rate, since the Orthodox and also the Assyrians and other Eastern Christians immerse themselves so heavily in the writings of all the early church fathers, and not just St. Augustine, who is the only Patristic figure most Western Christians have read, if they have read any at all, or the Reformers, and also, since the liturgy of the Eastern churches is attested to in the Second Century Strasbourg Papyrus, in a form that closely resembles the present form, in the case of the Alexandrian liturgy, known as the DIvine Liturgy of St. Mark to the Eastern Orthodox and as the Divine Liturgy of St. Cyril to the Copts and Syriac Orthodox (since St. Cyril of Alexandria had it translated into Coptic; the Bible had already been translated, but St. Cyril desired Copts to be able to understand the entire liturgy; this was in addition to his struggle against Nestorius and his opposition to Pelagianism and problems he experienced, such as a false accusation that he murdered the Pagan priestess Hypatia, and civil unrest among the Jews in Alexandria). This divine liturgy is very similar to the others in terms of the language it uses, the only unique aspect of it involving the fact that it has two Epicleses, which are part of the Eucharistic Prayer or Anaphora, specifically the prayers asking the Holy Spirit to make the bread and wine into the Body and Blood of our Lord, rather than the usual single prayer one finds in liturgies originating in Antioch. Indeed, the changes that occurred over time to the Eastern Orthodox and Oriental Orthodox liturgies are very well understood, as the liturgy is surprisingly well documented, and unlike in the case of certain apocryphal scriptural texts where we have lost them, such as most of the Gospel according to Peter, where only the Passion and Resurrection account survives, but it would be really interesting to have the entire thing, for what we know about it, it sounds much closer than the other “Gospels” such as those of Gnostic origin like the “Gospel of Truth” and so on, to the four canonical Gospels, and is a regular narrative, and not a sayings document, like the Gospel According to Thomas (which I believe is a Gnostic corruption of an authentic document, which is why most of the sayings correspond to the Synoptic Gospels, but there are a few sayings, and also the introduction or preface, which are obviously Gnostic).
But whereas I simply cannot access the latter and have no hope of doing so unless an archaeologist makes a breakthrough and finds it, or a forgotten copy of it turns up in a monastery on Mount Athos, or Tur Abdin, or in Egypt, or Syria, or Iraq, I am out of luck, in the case of the liturgies of the Eastern churches, we know how they were celebrated in the fourth century, we have liturgical texts from the second and third century which are consistent with it, and we know all of the changes made since then, and everything is documented to a great level of detail. What is more, of the major liturgies, in all of the traditional churches, not just the Orthodox, but also the Anglican and Catholic churches, most of the liturgy consists of Scriptural texts; in the case of the Eastern Orthodox Divine Liturgy of St. John Chrysostom, which is a recension of the older Liturgy of the Twelve Apostles historically used in Antioch, and still used by the Syriac Orthodox on occasion, 93% of it is of Scirptural provenance.
Furthermore, there have been no substantial changes in how the liturgy is actually celebrated since the thirteenth century, only relatively minor changes, such as the popularization of tonal four part harmony in the Slavonic churches. And the substantial change in the thirteenth century was the loss of the Cathedral Office at Hagia Sophia as a result of the Venetian conquest of the Byzantine Empire in the Fourth Crusade, which Venice organized ostensibly to try and overthrow the Muslims who had recaptured Jerusalem under Saladin, but after the fleet got underway, it diverted to Constantinople. This Crusade is also known as the False Crusade. At any rate, following this crusade, due to poverty, impending invasion by the Turks and other factors, those cathedrals that celebrated the Cathedral Office ceased doing so, but we still have that office; we know what it consisted of, and it could, and probably should, be restored, especially on that glorious day when we retake Constantinople, ideally by converting the Turks to Christianity (which I think is actually viable, considering the extent to which Erdogan was nearly overthrown a few years ago due to his Islamic fundamentalism and the relaxed nature of the Turkish people, many of whom subscribe to Sufi sects which are in some cases crypto-Gnostic, and also related to the broader family of Persian and Kurdish religions, which have Christian influences).
Owing to the principle of lex orandi, lex credendi, since the Orthodox and Assyrian liturgies have changed much less than the Western liturgies*
*These changed dramatically even in the late first millenium, when Charlemagne decided it would be a good thing to suppress the Gallican Rite and make the Roman Rite the standard liturgy throughout his Empire (I would argue that liturgical affairs were none of his business, but hey, he was the Emperor, and Frankocratia was a force to be reckoned with), and subsequent changes such as the introduction of the filioque, the use of unleavened bread, the requirement of clergy to be clean-shaven (historically, clergy were bearded, like the Orthodox), and the move towards Chrismation only occurring to the youths, and eventually, by the end of the first millenium, the laity being denied the Chalice and receiving the Eucharist only in one kind. The Protestants then changed the liturgy again, as did the Roman church itself, by discouraging the various regional uses of the Roman Rite and promoting the standard Tridentine liturgy and its predecessors such as the Dominican liturgy, which were developed for the same purpose of standardization, but in the case of the Dominicans, Carmelites, Norbertines and other friars, they had a need for it, since they might be reassigned to a church anywhere in the Roman Catholic world, and it was something of a bother learning the local liturgical customs; language differences limit the extent to which this is practical in Orthodoxy, even though there is no canonical reason why a Belarussian priest could not concelebrate with an Antiochian priest in Mexico City, for example.
Since we know to such a great extent the early liturgy and the current liturgy, and since the prayers are unchanged, we can assert the faith is unchanged, and from that, we can assert that the Eastern churches, including to a large extent even the Eastern Catholic churches, where in many cases there have been no changes made to the liturgy, or those that were, were largely rescinded after Vatican II (the exception being the Maronite liturgy, which was damaged even more severely than the Roman Rite in the wake of Vatican II). In general, the liturgies of the Byzantine Rite “Greek Catholic” churches are the least changed, being in most cases identical to the Eastern Orthodox liturgies except for the addition of some Roman Catholic saints on the liturgical calendar, some of whom are specifically Greek Catholic, for example, St. Josaphat of Ukraine, and perhaps the omission of one or two recent Eastern Orthdox saints, but surprisingly, St. Mark of Ephesus and St. Gregory Palamas are widely venerated, so the only real difference is that the Pope of Rome is prayed for in the litanies and commemorated in the DIptychs, which is actually proper, since these churches are under his jurisdiction, in the same way that, for example, the American Carpatho-Rusyn Orthodox Diocese, which is what we call an “autonomous church” (which really means semi-autonomous; a fully autonomous church is called autocephalous) under the Ecumenical Patriarchate in Constantinople pray for the Ecumenical Patriarch in their litanies and commemorate him in the Diptychs. Indeed, the Greek Catholics do not even include the filioque in their prayers.
So, if the law of prayer is the law of belief, lex orandi, lex credendi, and I believe it is, we can assert that the Eastern churches have changed the least. That said, it is also possible to identify churches which have moved closer to us, for example, High Church Anglicanism, and Lutheranism of the Evangelical Catholic variety. And early liturgical Methodism under John and Charles Wesley, and those liturgical methodist churches in the US, such as Epworth Chapel on the Green in Boise, Idaho.