WOW!! , LOTS of great shots posted this week!
Chris, The 50's was a great time for RRing

...unless your using Trainz to depict that time frame

...you are so limited as to what is available engine wise in the 50's. Steam is still good to use, F & E units, Fairbanks Morse engines, and GP7-9's, and Alco PA-B's, other then those, thats about all you have.
NO U50C's, 8500 series Gas Turbines, DD40AX's, and the list just goes on for miles

,
NOT a good time frame to do in Trainz if you like a large assortment of engines, but hey, its YOUR game, you can do whatever you want

.
PERSONALLY, I think if you like the older stuff, and just a touch of the newer, like SD40-2's, SD40's, GP's, U50C's, DD40AX's, 8500 Gas Turbines etc. , you might want to consider the late 60-70's. In the 60-70's there was STILL older engines on the rails, that was the time when you could see many older engines just before they were phased out, no steam though, unless it was an excursion run, just like today.
Like i mentioned before, I'm a bit of a UP History buff, i have TONS of books & DVD's on the UP, its taught me alot about what the UP had, how many they had, and when they ran them, but without that stuff you'll find
GOOGLE is your best friend as for what was running in what time frames.
I hope that helps
- Deano