master cylinder question
 

OK...

Going to be converting to rear disk brakes soon,
Im poor, so I am looking at using GM "mid size metric" calipers..
I plan on getting rid of the stock proportioning valve and putting in an adjustable one,
but I wonder about using the stock master cylinder in my 74 Road Runner..
Will I be OK using it with those calipers in the rear and stock ones up front?

I dont see a problem with that, I know quite a few people who have converted to rear disc with the factory master cylinder, one specifically in a 71 el camino and it stopped awesome with some "heavy" testing. Worst case you might have to upgrade the master later if the pedal is soft..