Well, I screwed up.
I received the new tuning keys I ordered for my Jag-Stang and attempted to install them.
They didn't fit, which should have been my first indication that I needed to send them back immediately. The holes for the Kluson tuners were too small to accommodate the barrels of the new locking tuners.
But, I wasn't that smart. I tried to enlarge the holes. It didn't seem like it would be that difficult.
I was wrong.
So now I've got a Jag-Stang neck with screwed-up uneven holes for tuners. A luthier with a drill press could probably fix it, routing out the holes to accommodate some even thicker tuners, but it might be cheaper just to buy a new neck. The project is on hold.
Sometimes it is possible to over-estimate ones own abilities, decide what you already have is not good enough, and try to improve it. I'd encourage any aspiring guitarists to be careful not to fall into this trap! It is probably better in many cases to simply hunt for a better guitar, instead of trying to modify one you've already got.
Embarassment and frustration all around! But more importantly, I don't have an instrument I can use to trigger my guitar synth, until I get this fixed or replaced in one way or another. That's the real frustration.