i would suggest not going with a disc/drum master cylinder when you have other better options available. i have a master cylinder/booster from an 89 wagoneer. it gives me trouble all the time. i dont have a proportioning valve, but i always have problems with rears locking up, then fronts locking up, uneven application, ect... after learning about the 77 'vette master cylinder i am inclined to swap it right in as soon as i get home.

-BrianM