Not saying he mightn't have seen that locomotive at some point, but here's what Taylor said about the nacelles:
My approach was to kind of "art-deco-size-it" in a way. I spent weeks drawing and re-drawing and designing the nacelles. I mean the front-end of the nacelles was almost a 40 Ford grille. But I tried to make it have a very art-deco feel; for example I added the parallel lines along the edge of the saucer.
March 09, 2001
Interview on Cinepixel
P.S. The locomotive in question is a C & O Chesapeake & Ohio M-1 Steam Turbine Locomotive.
Thank you for all that useful info. I was absolutely wondering about the train's identity.
It's odd that this Taylor guy gets such a modest credit for TMP at imdb.com, given that he played such a crucial role. I was expecting him to be the art director or production designer, but he's lost in a very long alphabetical list of people under Visual Effects. He designed the Refit and at imdb he's practically a name in the phone book!