If each of your OCs got to pick a time period to travel to, what time periods would it be and in which places? For the sake of this thought exercise we can pretend they have universal translators in their pockets or something.
Engie's is the easiest and likely the most well-known since she talks about it a lot: she has an intense desire to fight Alfred E. Perlman in a Denny's parking lot because she resents him for not setting aside any New York Central steam locomotives for preservation and scrapping them all. (We have so few survivors because of that.) I believe I've had her mention this desire on @ironhorsegirl a few times to varying degrees.
Conductor is also an easy one - he'd immediately jump to the 1930s to play with his favorite musicians. Being able to play trombone alongside Glenn Miller or in support of Cab Calloway would be a dream come true.
Fireman was obsessed with mountaineering as a kid and knowing her she'd want to be on a certain expedition so she could definitively know what happened to George Mallory and Andrew Irvine. She's haunted by the fact that no one knows if they summited or not.
AC is a bit torn. Part of her wants to see the far future, and another part of her wants to see the Japanese club scene of the 1980s because she loves the visual aesthetic and music. Perhaps she could try a bit of both.
Brakeman is honestly the hardest of the five to lock down here. His interests tend to be squarely planted in the present. But perhaps if you offered him a chance to be on the set of some of his favorite action movies to see how they were made, he'd be excited to take that opportunity.
