Ok, my memory is fogged by the rain we're having here, and my shop manual is doing a good job of hiding, but I will tell you what my '50 1/2 ton is like. This is the 'huck' type brake with the wheel cylinders that have the adjustment on them. The rear drum brakes have a cable that goes through the a hole in the backing plate at the bottom. It attaches to a nearly vertical arm in the brake that runs from down near the bottom of the brake up to a pivot point that the eccentric is attached to on the shoe (I'm a bit foggy here), and it engages a slot in the pushrod which connects to the other shoe horizontally. The other end of the cable attaches to the frame where it is connected by turnbuckles to the big pivot rod at the front of the bed on the frame. That connects to the pedal assembly in the cab.
If you are missing the pieces I'm sure mothertrucker can set you up. What you should really do is get a reprint of the original shop manual (see links in vendor section), which has nice pictures and tells you how to adjust the eccentric and the brakes. It's only about $25 and it really is a very good manual.
I had to replace my cables and they are hard to find. Fortunately I had my originals and I had my local speedometer shop make me some really good ones that are sheathed with rubber for $40 each. They are smooth and nice. The brakes work great now.
