73 up A bodies COULD have large bolt pattern.
Drum brake front=small bolt pattern.
73-up Disc front=large bolt pattern.
73 up A body 7.25 rear came with both bolt patterns.
73 up A body 8.25 rear was large bolt pattern only.
If you have an 8.75 now I'd get new axles (Dr.Diff)
and replace the rear brake assemblies with 10x2-1/2".
Donor can be from almost any 65 up rear end EXCEPT a body small bolt rear end.
You can also use the F,M,J disc brake assemblies for the front.
Either way you'll need the large ball joint upper control arms or the adapters to use the small ball joint.