Will 8-3/4 alxes fit in the old 65 7-1/4 rear?

IMHO, I'd keep my eye open for a complete pre '71 B-body 8 3/4. They are a little wider than an A-body housing, but you can make up for it with running more wheel offset. All you have to do is chisel off the spring perches and weld them to the position you need for your car.

I ran one in a '75 Dart Sport and I ran a '69 B-body Dana in my '71 Duster.