64 pete:
as a general rule, diesels want to spin slower than the gas engines we've got in these things. there are exceptions, but for the most part, this is the way it goes with truck engines.
a GM 6.2/6.5 might keep up with those old 216s i'd guess, but prob not a modern built 235/261. and they're HEAVY.
that being said, i've always liked the idea myself. cummins is a nice way to go. besides, it's not a DODGE engine (tho my daily driver cars have tended to be dodge), it's...... a generator engine, bulldozer engine, motorhome/bus engine... dodge just beat us to putting it into a 'normal' truck i guess.
i've looked at the diagrams for the 2-speed rear on my 2-ton - hell if i wanna swap gearsets in that thing even if there WAS another option! the books refer to a few diff ones, the 6.40/8.72 seems to be the 'nicest' for highway driving, and most common for the 1.5/2 ton.
i'd really like an external overdrive, stuck behind the trans. y settle for just throttle, gearshift, and 2-speed lever? MORE shifting!!