A pretty good source for a core engine might be a salvage yard that recycles old school buses, or Hertz/Avis/Ryder rental trucks. They were a popular power source for 1 1/2 ton and larger box trucks.
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!