I'm afraid those dual guage diesels in Utah are adjustable between standard gauge and 5-foot guage only. I think there were a bunch of engines built in the early part of the Cold War (remember that?) for possible use in Eastern Europe. And I suspect the WP&Y units are too big and heavy for the C&TS,
I think the best bet will be to locate a couple of 3-foot guage 65-ton GE's such as those used in steel mills. They were/are geared for low speed, use supportable Cummins engines and GE electrical components, and there are still quite a few around. The East Broad Top RR in Pennsylvania has one, M-7, which is used from time to time for work trains and for rescue missions as required. I believe there are two others "stored" at Rockhill Furnace. Parhaps a call to Mr. Kovalchick is in order.