For the rear brakes you may want to opt for an "adjustable proportioning valve". A
10 psi residual valve is needed in both the front and rear lines if the master cylinder is lower than the drum slave cylinders (2 psi residual valves are for use on disc brakes).... as shown in the diagrams at this link:
http://www.hot-rod.com.au/builder/brakes.htmlI did this on my two hot rods and it allows you to adjust the back brake pressure, basically adjusting the brakes so the front brakes don't lock up before the rear brakes. Hard to steer with the front brakes locked up.

Hope that helps!