1957-1961 Fake Stack Questions

This is probably Mike Trent territory, but will throw it out for all. Earl stated in some notes regarding the 16mm footage I sent, that he was pretty sure both 478 and 476 had the diamond stacks in 1957, as they were holdovers from the Jimmy Stewart Movie shot in the fall of 1957. In the film we see 478 with a straight stack on a train that is ridden. On this train there is also a baggage car behind the engine, and train appears to have stopped on the highline, as there is a shot of several patrons boarding the train as it is departing!
In the next visit, June 1961, 476 indeed sports a Diamond stack for a special out of Alamosa.
I had always thought the diamond stacks were in the early 1960's.
I guess Earl and I are wondering if this could have actually been 1956 for the Silverton train. In addition there are shots of 464 switching, and he said he thought it was retired in the early part of 1957??? Another oddity??
Yesterday I spoke to one of the guys who was on the trip, but was a teenager. He said when it comes to dates, we should defer to the NG experts, as they were bad about keeping notes!!!
Another question. Anyone have a date on a so-called June 1961 Illini RR Club Trip with 476 from Alamosa. This was an unusually short train.
Greg Scholl