If you could get a couple of narrow-gauge Mallets, I'd say model the Uintah- I've been on the old grade in a 4x4, and it was a doozy. Besides, the DRGW/C&S lines have been modeled to death,and I haven't seen much on the Uintah.
As for diesels, you could fudge on the URy's end-of-service date a...