When you have as much "stuff" as I do, packed in (mostly) category-labeled shoeboxes, you forget everything you have. This evening, I remembered that when I built my last gimbal (from scratch), I bought an extra motor as a spare. That motor, while not identical to the defective motor in the gimbal, is close enough to fit. Anyway, the gimbal motor that I ordered from Hobby King is the same type, so even that one would not be an identical replacement and would require the same modification.
So I did some measuring and drilling and Voila!, I now have a working gimbal. Now the motor coming from Hobby King will be a spare, and if I get a replacement from the Chinese guy that sent me the defective gimbal in the first place, I'll have two spares.