Roots on the Rails? Maybe go the other way and add in a few ticket-taking conductors, low-level train whistles, crossing bells, and distant coyote howls!
Only half kidding.. sounds like a cool project.
Keep in mind that a partial reduction of the extraneous noises, done in such a way as to keep things sounding as natural as possible, is likely to work far better than trying to completely eradicate the offending noise at the risk of damaging the valued attributes of the recordings. That said, these tools are ever-improving in their capability, and targeting the presumably frequency-specific brake-noise shouldn't be overly difficult.