The thing on the compressor is your governor. They fail quite regularly and I always keep a dozen of them on hand.

http://www.ryderfleetproducts.com/haldex-midland-kn18530/d2-air-governor-no-core-p-u55-kn18530

Your description is rather vague, but it sounds like your quick release valve. I keep a dozen of them on hand too.

http://www.ryderfleetproducts.com/haldex-midland-kn32005/valve-quick-release-3-8"-ports-p-u55-kn32005

Spring brakes were not required by law until Sept of 1975, but most larger trucks had them as far back as the 50's when they were invented by MGM. Although the parts may not look exactly like what you have, all components of an air brake system are still available

The governor cuts the compressor out at about 120 psi. When you step on the brakes, the foot valve http://www.ryderfleetproducts.com/haldex-midland-kn22150/valve-foot-p-u55-kn22150
sends air to the steering axle brakes and the relay valve for the drive axle. They look something like this. http://www.ryderfleetproducts.com/haldex-midland-kn28085x/valve-relay-plus-core-p-u55-kn28085x You should have a quick release in front and back to release air quickly when you let off the brakes. If you have room for spring brakes, I would highly recommend adding them. Nothing else will really old a truck except chock blocks.

A valve like this is used to operate the spring brakes.

http://www.ryderfleetproducts.com/haldex-midland-kn20021/valve-dash-pp1-hand-operated-p-u55-kn20021

It will pop out at about 60 PSI and set the brakes or of course you can operate it manually as a parking brake. I would forget about the old copper tubing they used and use nylon tubing.

http://www.ryderfleetproducts.com/velvac-20136/nylon-tubing-3-8"-p-u80-020136

If you are near something like a Fleetpride, they can fix you up with everything.