If the master cylinder is below the wheel cyliders or caliphers then you use a 10# RPV inline to drum brakes and 2# to disc brakes. This keeps them from sucking air around the seals or pucks as they retract and air entering the system. If the master is above the wheels then you don't need RPvalves. A disc drum master already has a RPV in the rear drum exit. Under the tapered brass seat where the line connects. You can check to see if there is one in the master by carefully inserting a paper clip into the master cly. brass line seat and feel for a rubber valve..
On a streetrod I always use the inline adjustable proportining valve, like Wildwood sells, in the rear line and I still think I could get away with not usining one on Disc-disc.
On my truck using the Fiesta booster I mounted it back on the trans. crossover after welding on a bracket then used the original pedal with a 2' extension to the booster. It's called streetrodding or IE; make it work. LOL