I have a 51 3100 with disc brakes on all four corners. The rear end is a 9" F**d with discs out of a 77 Lincoln. The same Lincoln donated it's 4 wheel disc master cylinder. I installed it with no power booster and have EXCELLENT brakes. The stock pedal to master cylinder mechanical advantage ratio really negates the need for power brakes. The pedal effort is the same as any of my modern vehicles with power brakes.
