The best options are the ones that are the most economically infeasible. Cummins intercooled 4BT. 30mpg and decent power. finding a place to stuff the intercooler in may somewhat "difficult", though. But if "I" were doing it, 5.7 Gen III all the way. That'd be fun one! Well, except for that whole installation thing!
:rofl:
Only thing I wonder about with a diesel would be the heat. Doghouse is pretty hot with the gas motor. First mod I made to my van was to install a sound deadener mat with a heat reflector on the engine side of the doghouse. $50 well spent.