These photos from the Library of Congress show two authentic looking steam locomotives engaged in a "Golden Spike" reenactment during the 1939 Worlds Fair in New York. Weren't the original Jupiter and 119 scrapped before 1939?

Yes, the original engines were long gone. These engines would be stand-ins. I'm not sure what engines were used in the East.On the West Coast during 1939 and 1940 there was the Golden Gate International Exposition that also had a performance celebrating the completion of the transcontential railroad. The Golden Gate International Exposition was held on Treasure Island in the middle of San Francisco Bay. There the completion of the transcontinential railroad was celebrated using 3-foot gauge equipment once used by the Nevada Central Railroad. This equipment was held for years by the Pacific Coast Chapter of the R&LHS and then contributed to the Calfiornia State Railroad Museum. The engines are a 4-4-0 and a 2-6-0; the cars are acombine and a special coach.

Some Web sources indicate Jupiter was played by the V&T #22 the "Inyo", and CB&Q 35 as 119 at the New York Word's Fair pagent.

At that time, V&T 22 was owned by Paramount Pictures, having been sold in 1937. Anothter V&T engine was also at the New York Worlds Fair's production "Railroads on Parade" -- this was the #21 "J.W. Bowker." The Bowker had been sold by the V&T in 1896 to a lumber operation; after the fair the engine also went througth the PCC/R&LHS to CSRM.