Swap in rear discs 70 Dart

DoctorDiff sells everything you need. 15/16” master cylinder, adjustable push rod. You can use the factory combination valve, or replace it completely with an adjustable one, or just plumb an adjustable valve into the rear line. Having an adjustable one will be better balanced if you tune it well, but plenty of people use the factory valve too. Depends on how your car is set up and how you drive it.