[MKS427]

You should be able to find a mile per hour calculator online that will give the best information for rear gear selection.
If you are considering rear diff replacement, I have a Torsen T2R-race version. It works great. However, it is not recommended to drag race with.
Glad you got your carb worked out. If you are going through multiple altitudes, like we do in Arizona, you may consider and EFI. When we get up to 7000' from 1200', everybody with an EFI doesn't have issues. It will take away a few top end HP, but the low end driveability is so much better.