I own a 1978 f-250 that is ready for a new engine. I would like to convert it into a diesel. Anyone have a recommendation as to a specific model?

In my opinion, it's way too much work.

Anything mechanical. 12 valve Cummins is very common. International DT 360(I'm working on putting one in a 94 F-350). Or good old International/Ford 6.9/7.3 IDI(least powerful out of the three I have suggested, but definitely the easiest).