Absolutely love the old striped crossing signals. I don't think I've ever seen a good shot of that particular set before. Unfortunately I can't help with the "when were those installed" question.
The Monarch signals were much more photographed, just because of all the excursions that ran that way and their more photogenic locations. At least one of them still survives in a local barn. Nathan Z. remembered seeing it from when he used to deliver industrial gas tanks down there years ago, and we stopped and asked permission to photograph it on the way down for the rotary run last year.