So much of this process of installing an air operated duel curcuit brake system seems to be an excersize in futility. This whole thing about custom made brackets, an expensive MC, another air tank, another airpak, more air lines, more plumbing, duplicating the later AF trucks, etc., is chasing-your-tail.
In reality, the "stock" duel curcuit system of the late trucks is just adding another layer of 65 year old thinking/parts/technology, on top of the first layer of 65 year old thinking/parts/technology. And now there is the up-keep of two expensive airpaks. It's just putting lipstick on a pig.
The thread that was started by Spicergear, and expanded upon by Jesusgatos, ran over a five year period, from '07>'13,and is the most complete and difinitive answer to having a modern, safe, high performance, duel brake system, at probably less overall cost.
http://www.steelsoldiers.com/showthread.php?16065-Hydro-Max-Brake-Assist-*pics-added*-(long-
Not only does this type of set-up give modern duel-curcuit braking, but also makes allowence for the addition of modern power steering, should one desire.
Back in the '20s, before the introduction of quality hydraulic systems/equipment, the Navy used air pressure to operate the ballast tank valves on submarines,, it took awhile, but when the hydra-tech stuff came along, the air operated systems were thrown by the wayside. Except for a horn, or fill a tire, or maybe pull a military trailer, there is really no reason for air, with its problems of leaks/moisture/lubrication.