Grego,
I have found a few references to the Silverton between 1964 and 1966.
Both trains seem to have had an open gon on the rear, (unless there was a chartered private car)and one of them had an open gon in the train.
From what I can tell, the set which contained baggage #126 also had the Alamosa, which was followed by the open gon. The set containing combine #212 had two open gons.
It'll take a slightly older fart than me to say if the practice of dropping the open car in the Fall was common or not.
Trento