Proportioning valve after conversion

The master cylinder makes no difference, it just makes the same line pressure for both F & R circuits. It simply affects the "leg muscle" to line pressure relationship.

Posts 4 & 5 are correct. Indeed, any change to the factory design can change the ideal proportioning - bigger rear wheels, different disc pads, ... Ideally, one installs an adjustable prop valve and adjusts it by skidding on a wet parking lot as post #5. I think no factory car has that and most think like posts #3 & 6, i.e. "good enough". I don't know that anyone has compared Kelsey-Hayes disk/drum w/ 73+ disk/drum. Probably "close enough" and certainly better than no prop valve.