i'd posted about this a couple years ago during my deployment, they've got a diesel dirtbike thats pretty much exclusively special forces and it has a pretty decent power/weight ratio. i wouldn't have had an issue sticking it in a trike since they were about a 650cc(it went fast enough for me) engine so some cutting and mods are about all it'd need. i know they made a smaller 400-450cc version but i've never ridden that one. nowadays im sure you can find a smaller one that wouldn't be much of a struggle to fit. but keep in mind a diesel bike would be more for work than fun because i doubt you'd need that much power doing anything other than hauling and drags
SAWFLY
It's not stolen, I just happen to have the same thing