I've done it with the China bike engines. You gotta match the transfers and turn the piston around, but it works really well.
Also had a buddy with a triumph that did it. I think that was a pretty popular mod, to have the exhaust coming out the back.
You could do it on pretty much any two stroke. It's better if you have a vertical cylinder. Having the carb on the bottom of a horizontal engine would seem like it wouldn't flow right, and it'd be sucking up a lot of dirt, and one good speed bump would smash it.
Here's a motorized bike I reversed: