[QUOTE=johnnymoparthe check valves you are talking about are usually 10# on the disc line and 2# on the rear lines. this will allow the rear brakes to activate before engaging the front brakes.
hope this helps.
Not true, the check valves are used in systems where the master cylinder is mounted below the floor. This is to prevent brake fluid from flowing back to the master cylinder out of the calipers. A proportioning valve is what controls the rear to front brake differential.
You must use a master cylinder designed for disc brakes, they are different from drum brake master cylinders. The difference is in the bore diameter of the master cylinder.