Based on the wild inconsistencies in the tenons, this thing certainly seems handmade.

I've got it mostly disassembled and sanded up to 220, debating between tung oil and shellac.

I'm also thinking of reinforcing the bow-back/seat joints by jamming some toothpicks into any gaps and then saturating with glue as much as possible. They aren't in terrible shape, just loose and I want to fix the laxity.

Overall I think things are going well so far

Looking good. I do like shellac as a finish

Is that main back piece just one piece of bent wood? Hard to tell from the photo, but looks like single bent grain.

Yeah it is

That's really cool. You don't see that very often.

There are some small cracks across the grain in that piece, but i figure if they were a big problem, it would've manifested sometime in the last 50 years, so I'm not terribly concerned