On the 1/2-ton Advance Design trucks I've dealt with, the brake plumbing is a little different than described above.
The master cylinder has two outlets. One feeds only the left front brake cylinder. The other feeds a Tee on the right, just behind the bellhousing crossmember, which splits to the right front brake cylinder, and to the hose feeding the two rear brake cylinders.
I ran all new lines so as not to be surprised by a failure later...
Most drum brake master cylinders have a residual valve built in to hold a little pressure against the brake springs. I've heard people say they did not use any valves at all but I added residual valves to my mine because the master is lower than the cylinders and calipers.
I used the combination valve from the vehicle I got my rear axle and rear brakes from, and used a disk kit that used the rotors and calipers from that same vehicle.
Seems to work well two and a half years and 10,000 miles later.
