The first 638 trip was not until the fall of 1960, and we have shots of that one. Most of the 638 trips were in 1961 and 1962, so I suspect this one fits in there. Try the May 6, 1961, and the May 6, 1962 trips, which were Denver Terminal Trackage. They are possibles, but just guessing.
Greg
PS We have a trip in 1959 with 647 that had Clerestory roof cars, and I think some Rio Grande cars. One of the coolest trips was May 12, 1963 when CB&Q 4960 ran a special Denver to Cheyenne, with a baggage car, coach, and business car 69. They did several runbys, and it looked like some nice shots were had on that one. This of course was after 638 had made it last run to Trinidad on Dec 16, 1962.