what master cylinder for disk/disk set up?

i was thinking of using an adjustable proportioning valve to tune in my rear brakes on my disc/disc set up. the earlier drum distribution block had a built in residual valve to keep a few pounds pressure on the brakes so air wouldnt seep in but with the new style wheel cylinders now days im not sure if its still seccessary. but anyway the junkyard should be full of drum/drum vehicles with decent distribution blocks.