The calipers are the same between the 73 up A-body disk brake and the B-body. The only part necessary from the B-body besides the larger diameter rotors are the caliper brackets that bolt to the spindle.
Carefull here. I have seen references that claim the piston diameter is different between the A-body and the B-body calipers. This could affect brake balance if you are using the stock proportioning valve. If you plan to use an adjustable prop valve, it shouldn't matter.
Also, there are two types of caliper attachment methods. One type uses pins as sliders, the other type the caliper slides in a groove machined into the mount. So the caliper type must match the caliper mounting bracket. Don't just assume you can just grab any old caliper and it will bolt right in.
