M/C question

I am in need for some information if someone may be able to help ... This is about master cylinder and for a race car .. My question is I have front disc and rear drum I am adding a M/C from a 78 corvette to the car and i have an adjustable proprtioning valve in my car .. Now the question is if the proportiong valve is opened to much will the rear drums get to much PSI and ruin something or will it be ok cause I am looking to use this so I can adjust my rear brakes on and off more less if I can and if not what set up would be good for that if any also is that M/C ok to be made for manule braking and I am only allowed stock M/C no after market styles,, has to come off a chevy car or truck ... Hope this is understandable on what I am asking thanks ....