I've got a bunch of Onan/Cummins engines stashed away, ones that got pulled from UPS vans when they retrofitted to a different engine. They're already set up with a Chevy 292 mount system, and a stovebolt bellhousing like was used on late-50's trucks with the hydraulic linkage. It's also got a Chevy-spline 12" clutch so a SM-420 or a New Process 235 will be a bolt-on fit.

UPS used them, along with 292's and Ford 300's interchangeably in their high-cube vans. The Diesel is 120 HP at 3,600 RPM, with a turbo. The first one's going into a F-350 flatbed, replacing a 351 Windsor/C-6 automatic, and the next one will probably go into my 59 Burb with a 3/4 ton Dana 60 rear axle and a 3/4 ton IFS from a later-model Chevy truck.
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!
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