This mod is compatible with the Railroad Engineer mod made by Jotrius.

Download it here:
https://www.gta5-mods.com/scripts/railroad-engineer

Install it, then open the provided "J10RailroadEngineer.ini" file.

Find the line "Train.Models" and add "freight3, yardm, warb" to it.

Find the line "Tram.Models" and add "metrotrain2" to it.

Make sure "Trains.EntranceType" is set to 0. If it's set to 1, you won't be able to enter the new locomotives.

Save the file.