I doubt the Z1s would have started receiving repaints until sometime in 1921, when the railroads were formally 'returned' from the USRA under provisions of the Esch Act.

I'm sure the NYCSHS has some documentation of how quickly the NYC, and probably some of the affiliated lines including the B&A, proceeded to repaint their power out of the hated USRA scheme after that date (but during the recession that was then prevailing).

I think you are correct to put them in the as-built "U.S." black. Be aware that some of the auxiliaries, like the headlight, may have been 'standard practice' that would be more or less quickly changed out for NYC's own favored practice after privatization -- there appear to be relatively few pictures of PRR trains during the USRA years but many locomotives were converted to carry smokebox-door-centered headlights that look very strange to those who don't expect them.

Oh my, which scale are you working in?

The USRA light 2-10-2 has been available in a couple of forms, some brass, and most notably as a mass produced model in plastic from Bachmann in HO scale. Sadly, it's been out of production for a number of years now.

A company called Sunset brought in a brass version of the engine in O scale.

https://brasstrains.com/classic/Product ... 10-2-Light

Good luck on finding the base model you need.

https://www.steamlocomotive.com/whyte/2 ... -laws2.jpg

I just realized these engines had Southern Valve Gear. Were there any other NYC engines with Southern Gear? How about after they were sold the CN? How many CN engines had Southern Valve Gear?

It's O scale I'm working in, actually got one of those Sunset USRA Santa Fes coming for the Z1 project. There is also a SP TW8 in O scale that keeps coming up, from Overland I think... Where that engine was nearly identical save cab, domes and cylinders to both the B&A and Fitchburg engines, it's just a matter of designing the replacement parts.