I think the gasline was a 1/8" or 5/32" microline, using compression fittings. It can easily be duplicated, plus some of the members here, and
PB Sports sells them.
A common mod in the old days was to remove the hose, and replace it with a traditional 1/8" NPT braided stainless line that feeds into the side of the valve, to a bottomline. (Make sure you allow movement, as the valve is supposed to slide).
They are not more complicated then a modern Tippmann 98. The difference is things are in different places. The bolt rod is external, held on with rubber bands, and on the left side, for example.
nick