I believe production was upgraded to a larger motor (Mabuchi RS-385) at some point. With the larger motor mounted vertically, the flywheel is thin and tiny, not a lot of room left in the crown sheet area. All of the ones I've seen personally had two tires, one on each side of the rear axle.
I think the chassis, cab, or some other parts of the train set locos are plastic, not die-cast. So they're not as heavy as the better separate-sale steam locos.
Honestly I would save your money and look at auction sites for one of the Legacy versions, like 6-11247. Avoid the batch that used Back-EMF for speed control; those weren't good runners at all!
