predator 212s do fit felt el guapos and maybe bixbys, and I know there are a few dyno frames that they'll fit in, but for the most part you'd be building your own frame.
you could maybe put it in the frame backwards and use a set of gears to reverse the rotation, sort of like happy time engines do, except on a jackshaft instead of built in.. this is something I've considered doing with a predator but just haven't had the time or money to do so. this method has it's pros and cons of course. pros being that the frame doesn't need to be so big, you can get some more of the gearing out of the way on the jackshaft, and the head of the engine doesn't point directly at your nether region. cons are added weight, cost, complexity, and parasitic power loss. I think there not being a piston flying at your junk at 300 miles per hour far outweighs the disadvantages.
I mean, not that I've ever heard of a piston shooting out of the head, but that would feel a bit like a .30-06 point blank straight into the testes, and I'm not taking any chances.
