Thanks, Tyler. Best of luck!
The plot thickens: There was one stud missing from the block! I have no idea how it kept running after that without damaging the piston, rod, or cylinder. It fired up fine before I tore everything down...
Spotting that missing case bolt may have saved my engine. There are a couple other small two strokes in pieces around the workbench, so hopefully I can salvage a stud and case screws from one of them.
Good thing I'm on holiday vacation.