I would clean it all up good with carb cleaner spray and some scotch brite. Break one of the rings and carefully use the broken piece to clean the ring lands in the piston. The carb spray will soften the carbon. Then lightly sand the cylinder with some 400 grit sandpaper. Clean it really good and put a new Frank Bowman ring in it. From what you describe, it should still make a good engine.

If you try the crockpot/antifreeze idea on the carbon, let me know how it works.

AV8TOR