Actually, Swamprat, technically yours isn't a "Fred Schultz" system. It's a much more rare- as far as I know, UK only- removable-tank Air America system.
I forget the details, but as I recall, the UK had some odd rules about HPA systems way back then, and one of the workarounds was to redesign the system to take the removable tanks (like a Max Flow.)
Internally it's identical, but the back half is female-threaded for the tank, rather than male-thread to attach to the bottle directly.
I looked around for one for quite a while back then, but they were impossible to find.
There was another old UK air system back then as I recall- was it an early Govnair? The tank was just a tank, and hooked to a seperate regulator via a high-pressure airline. That was another I wanted just for the novelty of it, but somebody told me they were horridly inconsistent and troubleprone.