Big bolt vs Small bolt

Big bolt is a 5 stud pattern, 4.5" across 2 studs. Same for the wheel pattern.

Small bolt pattern is a 5 stud pattern, 4" across 2 studs. Same for the wheel pattern.

An original A body 8 3/4 will be 5 x 4", aka Small Bolt Pattern.

There are numerous ways to make your original A body 8 3/4 rear into big bolt, such as purchasing new axles from companies like Moser or shortening original Big Bolt Pattern axles from another vehicle.