I recently bought a used XTM .18 engine with the intention of dropping it in a nitro sport that I had bought used cheap and never really used, after alot of inginuity I finally got the easy start to line up and hope it will work but my current snag is how to get the Traxxas clutch assembly to work on the shaft or the XTM, the Pro.15s nut has a long nose on it and cant screw on all the way, while I tried a clutch nut off a trx 25 engine but found the shaft doesnt extend through the gear. What can I do? Do I cut the shaft off? ths seems like a last resort to me and something that would just destroy a good engine but I dont have any other ideas. So can anybody help??

Yep you gotta cut it. You have to do the same thing to a long shaft O.S. 18 in order for it to work in an RC10GT/GT2.