I haven't run any diesels since May, so I guess I'm at least leaning towards pre 1954 on the Seaboard Air Line.
I have a few pieces of rolling stock I need to track down the build dates on, once I weed them out I'll probably give them and the diesels to my 2 grandsons.
I'm getting another Williams brass USRA 2-8-2 soon so that's going to pretty much seal my fate to steam only.