Proportioning valve

A factory proportioning valve is perfect when paired with the same combination of front brakes, rear brakes, and weight distribution it was used with. If you're using the exact same front and rear brakes as the donor car, and the donor car was an A-body, it's fine. The things that really need an adjustable valve are something that's significantly different from a factory combination - B body 11.75" rotors on an A-body, or swapping in an aluminum 4-banger and trying to give an A-body 50-50 weight distribution.