Fred,
This may take some more time to answer completely. But to jump right in I found this 1947 photo of the Silverton Mixed. At the end of the train is the Silver Vista a platform coach and the combine. It is a top down shot and I cannot see the roof walk.
I will look up 212 (Second) in my Annual No. 25 tonight to see if it lists when the roof walk was taken off. I suspect the roof walk was a left over when this 212 was really 215 and had the Pagosa Springs Coupla on it. Of course those numbers were swapped in 1942. So I would think sometime between 1942 and 1947 it was taken off.
But of course more research is needed to verify. I'll look tonight when I get home.
Kevin Cook