The easiest way is to find a 73 up A-body with disc brakes on the front. It doesn't matter what it is so your best bet for the cost is probably a Valiant or Dart 4 door. Then just take the parts off the doner car and use them on your car. There are lots of step by step guides out there on the net but basically you are just putting the newer parts on your car. Also a great time to completely rebuild the front suspension. I think you can find a car on craigslist for under $500 and there might be other parts you can use or resell. I got my motorless 73 Duster doner car for $350 and will probably get most of that back selling fenders, doors, etc keeping the suspension for myself.