Look what I found searching Craigslist.
From the article: "Plymouth locomotive collection. All or part for sale. 6 locomotives Model FHG, Hercules gas engine and plymouth (ERH) transmission, 36" narrow gauge, built in 1952. 66" width, 88" height, 5 ton each. Collection includes mine cars, wheels, steel dump box, some fresh painted. All restorable. GREAT COLLECTION. Call 303-358-0322"
Plymouth Locomotive Collection