[Big Dave]

Converting a gas engine to a diesel engine is an ambitious engineering project. Remember the GM 350 diesels? They had a lot more engineering resources than you and made one small but fatal error. Those Corvette head studs were not big enough for the violent diesel combustion event. The things had horrendous head gasket leaks til just before they went out of production. The 1986 engines had real diesel (20mm) studs and a high percentage of the cars with the 1986 350 diesel are still on the road today.

A much easier project is to convert the truck to a Cummins 4BT3.9 engine. You may have to modify motor mounts but otherwise it should be a bolt-up. There is a whole community of people who have done this and there is even a website for it.