Hi Eric,
Eureka's artwork was taken from tracings done on the locomotive and tender when it was stored at Warner Bros studios. Mr. Ron Steiner who was doing research back in the 1970s for the California State Railroad Museum went to Warner Bros and sanded through layers of studio paint to reach the original artwork applied by Baldwin Locomotive Works. He made full size tracings of the lettering and art work on the locomotive and tender, and took many color photographs (slides). Mr. Steiner took these colors and dimensions and applied them to the Sonoma when the CSRM was restoring that engine.
After he was through with his research on Eureka, Warner Bros sand blasted much of the engine and painted over the locomotive and tender in black.
After I got the locomotive and tender back in 1986 Mr. Steiner heard I was restoring it. He contacted me and asked if I was interested in having the original dimensions and art work that was on the equipment. I told him that I was, and he sent me the pounce patterns for everything along with many color slides that were taken during his research. I could not believe my good fortune !
So, what you see on Eureka and, Sonoma is 100% accurate in dimensions and color. When the Nevada State Railroad Museum restored Glenbrook, they asked me for some of my patterns, which were used on the Glenbrook as well. Of course the Glenbrook has some different art work, but that which are the same as on Eureka, came from Eureka.
I hope this answers your question.
Dan Markoff