Sell the A-body rear end for a lot of money and buy a B-bod rear for cheap. 1966 to 1970 B-body that is..
The B-body rear will have the right bolt pattern and will bolt right in with the Super Stock spring hanger kit. That setup will give you an extra inch on each side in the inner wheelwell for fat tires.
You will never find decent wheels for you car with the A-bod rear because of the weird bolt pattern,, 5 on 4"