I would look into Atlas trucks from their U series diesels and use an Atlas motor if you can get one or use a North West Short Line motor if not. Drive shafts can be made from styrene rod, but you'll have to modify them into a worm gear type setup.
I'm sorry for being vague as I have not personally made this mod, but I remotored a brass Oriental GP-20 with an Atlas motor and drive and it works like a champ with my Proto 2000 GP7's and GP9's that I remotored with Atlas motors and GP-35's and GP-40's from Atlas and Kato. I'm sure someone more knowledgeable with brass will chime in here and offer suggestions.
