Travo,
I'm not a big fan of your type of "Air Over Hydraulic" brakes. If you loose air there is nothing you can do except pull on the parking brake. My 1956 9200 has this type of system and I'm going to make it Full Air Brake truck so I can pull an air brake trailer.
Your system was not factory installed. The Air Over Hydraulic system that Chevrolet used was a complete hydraulic system with an Air Booster (similar to the Hydrovac vacuum booster). If you loose air in this system you still have brakes, you just have to push harder.
To make the truck safe I would convert to either Hydraulic with a booster (vacuum or air) or Full Air (change the backing plates out to "S-Cam with Maxi Brakes").
Since you have all of the hydraulic parts at the wheels it would be easy to find a brake pedal setup and go all hydraulic...how do you intend on using the truck?
Also, the system you have is not in the Chevrolet Shop Manual, however the wheel cylinders and shoes repair info will be.
Mike B
