Not sure; I'm only guessing at around 9:1. I'm curious to see the piston and cylinder. I'm wondering if the skirt is too short, which caused rocking and scoring. If that's the case, a new piston and cylinder will be a temporary fix, but it will certainly run well enough to sell it. That said, I'd never stick a buyer like that without first explaining the situation.
Once you have the head removed, we can get a better idea of which gaskets would fit. Pics please.
