This evening, I finally found time to test out the super-thin motor leads for #10. It looks like they should work.
First I installed the motor, and verified that there were no shorts between the frames and either lead. The most likely failure here would have been at the gearbox flange, where the tissue paper and copper foil sandwich overhangs the end of the flywheel assembly.
Then I put the boiler back on. Due to a reinforcing flange on the inside of the boiler where the smokebox broke off during assembly, it is challenging to get the motor to slide in. However, when at last I had coaxed it into position, and seated the boiler on the cylinder saddle, I found no shorts once again.
So, I took everything apart again, and soldered the motor leads to the motor. Then, while the soldering iron was warm, and the mood was upon me, I started soldering the leads for the new decoder.
This is a LokSound Micro Select, and if I’d read the manual, perhaps I would have stuck with Soundtraxx. LokSound decoders synchronize the chuff with magnets rather than with a cam, and #10 has a cam. I left the wires a bit long just in case it really bugs me and I wind up swapping it in the future.