looking for 73-76 a body disc brakes

The spindles from a 73-76 A body OR a 73-74 E body will bolt right to the existing upper and lower control arms on a 64-72 b body. The 73-76 b bodies changed the entire front suspension with different arms. For the pre-72 B body, it's the easiest swap in the world. If you want to go all-out and use the big police rotors you simply change caliper brackets.
This article helps a lot.
http://www.moparaction.com/tech/archive/disc-main.html