Greg,
I found three more books of Dad's pictures.
I may have your date. Although I don't have any pictures of the consist, I do have several pictures of #638 in Denver, preparing for what my Dad wrote was the last Rocky Mountain RR Club trip behind #638, on November 14, 1962. You said that there was an NHRS drumhead on the rear of car 96, if so either my Dad was wrong about the sponser of the train or this is a different train. The RMRRC was not the NHRS. The train ran to Golden, and the engine was fitted with a tall spark arrestor. I'm sure Dad rode the train, but didn't take any pictures on the trip.
Here are other fan trips and specials on the C&S in the books I looked at today, I believe the pictures Scott sent are related to the Jeffco School specials in May 1962, although none of the pictures I have taken in Boulder show a business car on the end.
The only excursions listed below that I do not have pictures of the consist are the Rotary Club trip to Boulder, the RMRRC trip described above to Golden, and the last run to Trinidad. You can eliminate all these others.
4/9/58 #646 to Golden
6/6/58 #902 to Cheyenne (California Charter train)
7/27/58 #900 to Cheyenne
8/24/58 #646 to Lyons
10/2/60 #638 to Ft. Collins (Rio Grande Coaches in consist)
9/10/61 #638 to Ft. Collins
5/14/62 #638 Jefferson County (Jeffco) School Special to Longmont
5/16/62 #638 Jeffco School Special to Longmont
5/17/62 #638 Jeffco School Special to Longmont
5/18/62 #638 Final Jeffco School Special to Longmont
6/8/62 #638 Illinois Railfans Charter Trip to Cheyenne
7/27/62 #638 to Lyons
9/9/62 #638 to Boulder Rotary Club Special
11/14/62 #638 Last Rocky Mtn. RR Club trip to Golden
12/16/62 #638 to Trinidad.
