The 464 was also still in Durango until 6/73 as you can see from this photo in pretty sad shape...
The 499 and 491 (donated to the Colorado Historical society) stayed in Alamosa until 6/85 when they were trucked to Durango and Golden respectively. I think the 499 was part of the equipment set aside for Phil Anschutz but I believe only caboose 04343 went to his ranch in Weld County at the same time the engines moved out. 480, 493 & 498 were part of the Silverton sale to Bradsaw and were moved in 1981 (a photo of the 493 arriving in Durango was posted recently by Fritz Klinke). The 486 went to the Royal Gorge in 1967 according to the information posted on the Steam Locomotive site linked here where you can search for any steam engine.
So your Durango circa 1968 roster:
464, 473, 476, 478, 481, 497, & I think #50 might still have been there