I personaly run a 72 Vette master and tossed all proportioning...it works because of caliper systems.
14 Bolts front and rear 10.5" ring gear former full float.
14" rotors with 4 piston wilwood fronts, but little ford explorer style brakes rear.
Most times when I'm building jeeps w 1 tons, I use the oem master and never have problems. It's only when asked to upgrade that I look at 97 dodge 2500 master or Vette.

I'd run the stocker if it's ok and has not been left empty/dry.

SD