You could find some factory disc brake spindles from a 73 and up E or A body, and use all factory stuff. Using those spindles, you could get some 11.75 rotors, find some caliper adapters for pin type calipers, and use factory calipers. The back brakes will be fine like they are. If there's nothing wrong with your upper control arms....put new bushings and ball joints in them and use them. There are a few places you can buy a flywheel that is balanced for the Magnum, and has the notches cut in it to trigger the ignition. Hotwire Auto in Arkansas sells a conversion harness to use the EFI that is already on the Magnum. Good luck.