I have discovered (I think) the reasons my brakes are so bad on my 1962 300H Chrysler is (a.) the factory specified dual diaphragm booster had been replaced with a NAPA alleged replacement single diaphragm booster, and (2.) the assembled clearance between the rod sticking out of the booster and into the master brake cylinder was .31 inches, causing the pedal to be way too low initially.
My factory shop manual says this is a factory adjustment and don’t adjust it. What should that clearance? I have brought ot down from .31 to.06, raising the pedal considerably.