Detroit 2 stroke engines need gears- - - - -lots of them- - - - -since the effective torque band is so narrow. You'll need a gear for every 400 RPM since the useful torque range is from 1750-2150. They're also HEAVY, so anything less than a 1 ton truck is probably going to be extremely nose-heavy and the front wheel bearings and springs are probably going to be overloaded. After everything is sorted out and working, you'll have a noisy, stinky, heavy, slow truck you have to row with the shift lever(s). Have fun, but that sounds like a masochist's pipe dream!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!