A steel Aerox D with CGA540 is what you want. I keep one in the glider and another clamped into the trailer.
Currently listed as a closeout item on Wings And Wheels.
Then look on the ASW27 newsgroup for my mods to get the seat to go all the way back with the O2 cylinder in place.
Jim

http://wingsandwheels.com/used-close...540-valve.html