Pure BS. There were a couple of un-authorized motor car runs west of Chama, but no locomotives went that way. It would have been insanely stupid to run on uninspected track. If they put an engine one the ground. It would have all been over. One of the guys who went on a guerilla speeder ride told me they had to go through lots of fences and that all the crossings were paved over. They carried their motor car over the crossings. Can't do that with an engine. There was a story about rescuing the MW-02 from out near Monero on one of these junkets.
I've never seen any documentation of 492 being fired up. 487 was fired up in the spring of 1971 to do some switching while 483 and 484 were stripped for flue extension. Pics of 487 hot do exist.
One of the earliest proposals to save a portion of the NG was to save the Chama-Dulce portion. The Jicarilla Apaches were behind this proposal, but it never gained any traction.