wanted 8 3/4 rear end

I have not personally done it, but apparently lots of guys have put the B-body rearend into an A-body with a little tweaking and a different off-set on the rear wheels. Save your money and time and take a look at it as an option. If you're not interested in that, then take look at getting the housing and perches modified on the housing that you have.Probably quicker and faster than finding a gold plated A-body housing.
Daryl