I only have one loco with original wheels. It has the number "12" on both geared wheels, and no number on the plain wheels.
The motor you have looks like a perfect fit for my dark green 9. I bought the 9 set from the original owner's son a few years ago and haven't got around to rewheeling it. I was hoping to find some original wheels.
Here's a shot of the motor and the way the reverse switch indexes with the switch on the body:
Because this is a 9 not a 9U the motor mounts with 4 screws inside the body. A 9U has clips to remove the motor. You can see the number 7 on the armature.
Here's the switch on the outside:
The 381U has the same switch, so does the orange 9U. That reverse switch is also used on the hand reverse 384 and 390 steamers, but the wheels would have threaded holes for valve gear.
