July 1963 is probably correct. 473 has a red background on the spot plate, a 1963 feature only. 473 got new paint in Durango before the 1963 season started, she still looks good. The track 498 is sitting was was cut off in the spring of 1963 when the reverse loop was relined to connect with the depot track just north of the roundhouse.
1963 was the first year of "Rio Grande Land" and the D&RGW truly promoting the Silverton Branch. Two new passenger coaches were built in Burnham the winter before and early in the season the first 3 open gondolas showed up, although one may have been without a roof. This created a 15 car train which was more than one K-28 could pull. So a second train was created by fitting out baggage 126 as a snack car and splitting the consist into two trains.
In 1963, the train ran in two sections with the first train carrying green flags. I believe the next year, the second train ran as a timetable scheduled train.