what master cylinder for disk/disk set up?

i was planning on using an adjustable valve for the tuning or the rear brakes so would this take the place of the combination valve? i thought drum brake combination valves had a built in 10lb residual valve to hold the brakes out so theyre ready to grab which would be no good for discs? the MC iv been looking at has a 1.06" bore so would this be too big then? another one was .875". thanks for all the info guys i was hoping to get a MC today but i dont think ill have time.