As I understand it the period of the movie is about 1869. Somehow a K just doesn't fit. Oh well.
When Ken Burns filmed "The West" for PBS they had the good historical sense to use Eureka for the Central Pacific scenes.....maybe not the right gauge, but at least the right period locomotive, but then who is taking gauge measurements anyway. In any event, Eureka did run in the Sierra Nevada mountains for some 35 years when on the Sierra Nevada Wood & Lumber line after leaving the E&P.
Oh Hollywood (or wherever)...will they ever get it right? Next thing ya know, we will see some growler with a fake stack on it and fake steam pouring forth.
Dan