Barring blind drivers, most Northerns (4-8-4's) need 72" radius. If it is 2 rail, a rectifier (converts AC to DC) should run it (Williams made both 2 and 3 rail versions). If it has pickup rollers, it is 3 rail, and you will need a transformer, and are on the wrong forum.
I don't recommend plastic wheels on cars for 2 rail operation, as they leave crud on your track.
What it will pull, you will need to test.
Good Luck!
ECI