master cylinder part #

need some help trying to figure out what master cylinder to use.i just picked up a 71 demon with a 440 4 speed i am redoing the brakes.come to find out it has a front disc set up from a 73 74 a body rear brakes are 10 by 1 3/4 im thinking it should be 9 " rear brakes by the vin this demon started out as a 318 3 speed trans. this is a manual brake car