Pulled the plate jewel for the balance out of the parts watch and very carefully installed it into Jeff's. Easier than I expected. Used the new balance and it's jewel's entire assembly. It almost works. I'm going to clean it and oil it with a reasonable amount of thin oil.

EBay sale. Total $49.61

Serial #29977190

Model 3, 1919, 12s, 17j, railroad, nickel plate.

Serial #21280987

Pretty easy to get apart. The only thing I disassembled was the balance assembly. In the pictures below we see the face (dial in excellent shape), the back with deer, the movement, the engraving "Father to Walter, 6-7-19". The end of the hairspring broke off--I'm not sure if this is something I can fix, it's so tiny. YouTube time. The next image is the bottom jewel, very definitely broken; top jewel looks fine. The last image is the two ends of the balance staff--left one fine, right one definitely broken.

EBay has plenty of these, it's just a matter of making sure they're exactly right, and that the correct parts are OK. For example, this one would be great except that the staff is broken, no idea about the hairspring. It might be worthwhile to get one like this so long as the bidding doesn't get too high. Have the working watch plus a spare for parts.

Model 15, 1918, railroad, 16s, 21j, nickel plate.

A bit hard to get the front to unscrew, but it came away. In the pictures we see the front--dial in great shape, the movement, then partially disassembled. (Last picture is for the serial number.) First thing I found was the mainspring wasn't winding. I was able to fix this (I think) by bending the spring in a little--I won't know for sure until I can wind the watch all the way up. As for the jewels, I'm not great at telling if the jewels are OK--I think these are, but dirty. With the staff, you can see the right side is broken.

This one is a little harder to find on EBay, though I'll track a couple bids on whole, functioning watches and see what they go for.