It depends on your master cylinder. A disc / disc m/c will need a valve for front & rear. A disc / drum m/c will only need a valve in the front line.
I have a m/c from a 79 Mustang in my 1949 - 3100 with drums front & rear. The stopping is much improved over the stock system, but I will be adding discs to the front later.


1949 chev 3100 3 window. 350hp/327/m21 4 spd, 12 bolt rear, power brakes, 3" dropped axle from Sid's. Disc brakes next.