If you're not concerned about keeping the loco original, I would substitute an MPC-era integral motor/truck. You would get two powered axles instead of one, and two traction tires. Add some stick-on lead weights and it should pull pretty well. MPC diesels get a bum rap because of the nylon gears, but my 8361 survived a decade of childhood abuse and ran well into my adulthood. It even stayed on the rails when 8' of water flooded our basement and our platform floated up to the rafters!
If your really want to get fancy, you could cut a bigger hole in the front, and add a second MPC-era integral motor truck. With 8-wheel drive and 100% of the weight on driven wheels, it would pull like a mule AND run smoother, because you would be getting twice as many power pulses per inch. You can only do this with the MPC motors, because all of the postwar motor trucks lack pickup rollers- you need a non-powered truck for the rollers.
Did any of the 200-series Alcos have two powered axles and Magne-Traction? And +1 to what Brianel said about using MPC-era cars with fast-angle wheels.
