To answer the other part of your question about the D&RGW loco's that were Duel Gauge equiped...
It depends on "when" you ask the question.
The 496 seemed to have kept her due gauge coupler most of her life. In fact the 496's Tender, now behind the 494 in Antonito still has the tri-way coupler pocket on it.
I have seen photos of the 492 and 488 when stationed in Salida with the tri-way couplers. I don't remember the dates on these photos - although I do remember they were taken for the Flying Rio Grande paint scheme which means prior to 1940-41.
I am sure there were others so equipped - I do not have a complete list though.
Kevin