So... slowly moving forward (the speed of all my projects)...
This is the "test" I got back from the old school machinist:
He put the whole thing in the lathe (gripped it by its teeth, I assume) to trim some of the taper around the shaft area, then used that new surface to hold it in a chuck and remove the teeth.
Here's what it used to look like. The modified gear is the output one (on the left) in this pic of Ben's:
So the word from my brother is the machinist is willing & able. So I'll go out to see him with the rest of the parts to talk turkey. And money.