The Onan engine is a little heavier than the stovebolt 6. I sold one to a guy who put it into a CJ-7 Jeep, so other than adding a few spring leaves, you probably wouldn't have much of a problem adapting it. I definitely wouldn't try it with one of the wuss IFS suspensions like a M-II. A Diesel engine is for serious truckers, not somebody with a pantywaist street rod.
Jerry