April Fool's!
Wait, sorry, it's not April yet. I'm afraid you've fallen for a very old confusion in railfan circles: there are two completely different Jupiters. The one we're talking about is Santa Cruz Ry. #3, a narrow gauge Baldwin product that ran in California. The Golden Spike "Jupiter" (Central Pacific #60) was standard gauge and it was scrapped in 1909. (incidentally, UP #119 was scrapped the same year) Muddying the waters is the fact that other engines, such as the "Inyo" and "Sonoma," have 'played' the "Jupiter" in Golden Spike reenactions for years.
A lot of people get the two mixed up. I was talking to a friend about my 2003 trip to Utah and he asked me why the NPS built a replica instead of just getting the original from the Smithsonian!