The creation date of the Hebrew calander is the creation of Adam and Eve from Adam. So it is not the creation date of the Creation, but of Adam and Eve. And according to what I read, that calander was introduced in 359 A.D., and the Hebrews say it begins with the day of creation.
The conversion is a straight year to year comparison. You may not agree with that, but that is how I do it. And everything that I plug in seems to fit perfectly. So I will consider it accurate until something shows up to change my mind.
And if I go here
http://www.fourmilab.ch/documents/calendar/ to convert the dates they still match up.
So in the overall picture I am doing it in the correct manner, as far as I can tell.
Year 0 on the Hebrew is 3760 B.C., and year 7000 H is 3240 A.D..
Just as it should be.
As for convincing you about the creation date, are you referring to the entire Creation or the creation of Adam and Eve? The two are separated by quite a bit of time, and I have no idea about the beginning date of the entire Creation. As far as I can tell it could be anywhere from several 24-hour days to several billion years before Adam was split.
I would guess several hundreds to several billions.
And yes, they probably were wondering what the Great Pyramid was actually there for, and how it got there.