So, something interesting occured, which is going to be hugely beneficial not just for whoever decides to use this, but also for me doing this sort of thing, which will allow this mod to be done purely via LoS and RED.

An updated 2.0.0 version of this mod will come out once the LoS update is rolled out, which will (require you to respawn everything, as usual) include changed identifiers and names that should make finding these cars easier, as well as hopefully implement new cars, made from the 1893 Pullman coaches.