brake help

[prostreet1967]

i have four wheel disc on my truck i have a booster master cylinder and combination valve off of a mid 90s chevy truck. seems like rear brakes drag pedal is spongy bleed several times. i read on mp brakes site that disc/drum master cylinders have built in residual valves that will cause rear brakes to drag in disc disc situation.

i wanna go back to manual brakes so i need a master cylinder for manual brakes and 4 wheel disc. anyone know of something i can use from auto parts store. would rather not have to order one right now but if thats my only option what would be a good one.

thanks