---"Even if it were just a custom shop, build on demand type of thing, using standard 2100 pump parts, it would be better---"
Bad ju-ju! The 2100/2200 pump rods have always had those *&^%$ compressible plastic links. Early models the compressible links were only a bit over half of overall length of the pump rod but in current production the whole thing is made of plastic. To make them more efficient a switch to an adjustable pump rod with a flat-faced o-ringed piston matched to a flat-topped valve makes them a different animal if you can eliminate additional losses between the pump face and pellet skirt. Tom