NG is probably the most abundant fuel right now and cheap, worth considering. Your swamp buggy sounds like a fun project!
It started out as a mid 60’s GM 2 ton cabover truck with a 6 cylinder 4 stroke diesel, I removed the cab, the axles and basically everything but the engine and tranny.
Fitted a pair of military Rockwells with 12” inches of lift, a NP 205 transfer case and I’m about to get a 1994 Ford F-350 quad cab on it soon, and I fabricated rims for 55” tractor tires that work just right with the 6.72 gear ratio top loaders.
maybe next year I’ll build another but running solely on steam over a hydrostatic drive. Think running gear from a Bobcat mated to eather a high pressure steam turban or a standard steam piston engine evolved from a large industrial air compressor I have lying around.
And if I do get it running I’ll make sure the world knows about it, belching smoke from clear cutting old growth trees, should explode a couple hundred thousand liberal heads at the least.