Indeed an interesting game, and while we think of the Colorado 3 footers as having similar needs, and roughly similar conditions and standards, and thus benefitting potentially from USRA standardized designs, there were also the various 3 foot lines of the Milwaukee Road, Chicago& North Western, the Hawaii lines, and others that I cannot recall off hand, not to mention the EBT and perhaps the Pennsylvania Railroad's 3 foot lines although those were standard gauged at some point, perhaps prior to the war? Certainly the CNW's 3 foot lines could not have hosted even some of the modest sized Rio Grande narrow gauge steam.
I have never read that the USRA was as ruthless about shutting down duplicative or failing 3 foot lines as they were standard gauge railroads and perhaps they just were not strategic enough. But part of the game could also be to envision a rationalization of the 3 foot systems.
It is worth noting that the USRA didn't just design locomotives, it also grabbed stuff from loco builders, such as the Russian decapods and some French consolidations, and sent them to US railroads. So in addition to your speculation about some use of the USRA switcher boilers as standards, I wonder if the loco builders had foreign narrow gauge steam on their factory floors or in their catalogs that would have been decided on as a standard or series of standards? I could envision some narow gauge equivalent of the USRA's "heavy" and "light" distinctions.
Dave Nelson
Back when I was playing with Hon3 the question came up of what the USRA would have done if they decided to have a standard design for narrow gauge (3’). The game isn’t whether they would or would not produce a design. They didn’t, and with good reason, but were one key resource away from plausibility with the miles of narrow gauge still in use in 1917. So if given the task, what would they have done?
1) Clean sheet designs but in the USRA “style”?
2) Use whatever modules they could from the existing designs? Things like steam chests, valve gear, firebox. I could see the 0-6-0 boiler as a starting point for an outside frame 2-8-2, as a modeler I might just change the length of the smokebox as needed. Would the 0-8-0 boiler be too heavy for a Mike? Would they want an articulated such as a 2-6-6-2? A 2-10-2 if the lateral motion was enough?
3) Anoint a few models from a major builders catalog.
4) Something I’m not smart enough to think of?
Maybe no one cares at this date, but it would be fun to see what solutions people would come up with.