610 and 1702 are both USATC S160 class 2-8-0s. 1702 was built in 1942, 610 was built in 1952. Because it was built at a different time, 610 has some modifications to the design, such as larger cylinders and smaller drivers. When comparing as built photos of each it would be hard to tell them apart.
Since they were built, they have been modified in appearance. 1702 has its headlight in the center of the smokebox front with the bell hanging above it. 610 also has a centered headlight, but the bell is located on the fireman's side below the pilot deck. 610's air compressor is located on the fireman's side at roughly the midpoint of the locomotive, while 1702's is located behind a shield on the pilot deck. TVRM rebuilt 610 with a new cab around 1990. At the same time, the single dome was split into a steam and sand dome. 1702 doesn't have either of those changes.
Cheers,
Ben