The Trainphone became more prominent during WWII so would not have been seen except on test cars a few years prior to the war. The black roof was on some cabins between the mid-40s and 1955, when black roofs and keystone became part of the standard paint scheme. The pre-'55 paint scheme lasted many years after '55 because there were a lot of cabins to paint.
The chrome yellow paint on handrails started in Jan 1949. Prior to that they were the color of the car or sometimes black. Because this was a safety mandate, I assume the handrail paint was completed quickly.
Cabins had no keystones (except the N8) prior to '55. Since it takes time to paint a large fleet, some cabins did not get the keystone until years later.
So, this car is prototypical for your steamers from Jan 49 through the end of steam (1957 with some kept as backup until 1959).
If you paint the handrails the color of the car (I have done this), this car would be good back to WWII.
Or you could not worry about it and run your railroad any way you like. As they say, it's your railroad and please enjoy it.