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.