Whatever powerplant you end up choosing, I'd strongly suggest including a heavy duty automatic transmission in the package that's compatible with the engine. It's a lot simpler to make a shift selector from a push-pull cable similar to a PTO cable, than the Rube Goldberg mechanical linkage necessary to shift a manual transmission located several feet from the driver!
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!