Cool project. You'd think something like that would be marketed/produced by Crosman or some other company.Maybe in the 392 price range, but with the modabiliy of a 1322 and rail for a scope.
I built a Discovery .22/ 392 hybrid a few years back. It produced 900+ FPS on 10 pumps with 14.3 grain Premiers. My tuned 392 produces the same power level but I thought the Discovery version was a lot more versatile. I decided not to put a pump-tube conversion kit for the Discovery into production because they were going to cost too much to produce for what I think people would be willing to pay for them. If it was a break even situation I would do it just to expand the market but it was going to be a big loss.