Okay finally did this on the actual guitar. Something of an anticlimax, but I think I'm good, at least for now.
I soaked a Q-Tip in thin super glue and wiped it on the inside of the pocket where the crack ends. I let it cure a while, scraped out the excess glue from the pocket with a razor blade, and then repeated the process a few times. I even got right up to the top edge of the pocket where the top meets the pocket. I covered nearby areas with wax paper to avoid accidentally dropping glue anywhere I didn't want it.
The result? I am sure some glue must have gotten in the crack, but visually I can't tell any difference whatsoever. The crack is just so tight.
If even a tiny bit of glue got in there, it should be enough to keep the crack steady. There's also a tiny bit of glue on the top just right along the edge of the pocket.
It might be possible to make the crack less visible by dropping glue from above and buffing out, but I'm not going to try that unless the crack grows at all for any reason. I'll keep an eye on it and be careful fitting the neck (scraping out the pocket more if needed), but I don't think it's going to move at all.
I did experiment using some foam-tip swabs, but they didn't work as well and still had a similar reaction as the cotton Q-Tips. The weird smoking reaction didn't seem to happen as much this time- I may have used more (or maybe less??) superglue on the swab. No idea, but didn't burn my house down or scorch the guitar or anything.
Thanks everyone for the help and input here!
