71 vs 73 disc brakes

Ok guys what is the difference in 71 and 73 A body disc brakes. Bolt pattern I know. Are the other other parts such as control arms and such interchangeable? I bought a 73 340 k member for my six cyl 73 Dart. I got LCA with it. I have access to a 71 dart with disc brakes for parts. Any thoughts. Thanks.