Shortbus rider checking in!
If other people are driving it, get a gasser. Diesel will be a nightmare if you're not in control of it, and someone will fill it with gas eventually.
They say a Chevy runs right for a short time, and wrong for a long time.
Can you get a Chevy 2500 truck and slap on box on it? We have done terrible, terrible things to my dad's '98 Silverado 2500 and it still goes strong.
Avoid the Ford Triton engines, their spark plugs weld into the head.