I really didn't read the entire post but first thing, do a compression test.
Could be a broken ring land or cracked piston.
Typically a minor piston break doesn't cause any bore damage.
On budget repairs I've seen single pistons replaced. Quick hand hone. New rings. Slap another piston in and be done.
However most do a full rebuild and upgrade.
You might even get a used piston for free from someone.

Just considering the options. Let us know!