There was an outfit from Finland (I think) making an engine reverse kit for a while but they don't seem to be available any more. It was basically a forward/reverse recoil starter, a fancy chip to change the timing, and a template to modify the secondary helix. Had to shut down the engine, flip a lever, then start back up in reverse.
I won't say putting a reverse Diamond drive from 07/08 in it is impossible....but it would be a ton of work. Reverse case doesn't fit the non-reverse case hole in the bulkhead so you'd have to find a way to change it accurately. Outside edge of track clips and rubber nubs won't clear the case so you'd have to cut them all down. Electrical system probably not compatible with the reverse shifting motor, but you could fabricate a manual actuator. I don't know anyone that's actually attempted it after figuring out how much work it is. :d