Exchange Diesel Engines
A good site for those considering a conversion or just an exchange engine: Dealers Diesel Quality Remanufactured Diesel Engines They have Ford/Navistar, Cummins B & C, and Cats. I bought a damaged Ford truck with one of their engines and put it in my old RV. Still running well.
Also good for comparing prices for what a overhaul might cost.
The Fords from 1988-92 are mechanical engines, some with turbos. That is the engine I used (56E8D190U). Could replace the gas Ford in early models.