Also, in regards to the indwelling of the Holy Spirit within the Old Testament saints: What do you make of Genesis 41:38, Numbers 27:18, Isaiah 63:11, Ezekiel 11:19, and Ezekiel 36:26-27?
In addition, while John 14:23 is not talking about the indwelling of the Holy Spirit, it does show that both God the Father and the Son of God had the capacity to indwell believers before Christ's crucifixion (Which would have been the time of the Old Covenant still). For Jesus essentially says that both the Father and the Son were able to make their abode (or home) within a person if they love God by keeping His words.
"Jesus answered and said unto him, If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him." (John 14:23).
...