A couple things I've noted on my brake system installs. Trying to use a salvage yard proportioning valve and getting your system properly bled and dialed in so you control rear drum lockup, especially with a boosted system, is a problem.
I've found that using an adjustable proportioning valve, in combination with the 2 & 10 pound residual valves will save you from a lot of rear brake lock-up headaches.
ECI, Master Power brakes and CPP offer some good insights but have a tendency to push their own pricey combo and proportioning valves. These same valves (Wilwood) are available from Summit/Jeg's for a much better price and let YOU dial in the brake bias based on your own driving conditions and preferences. I have pics of my valve setup in my album. Hope this helps.
Dave
