While you have the head off, cut the ridge, hone or break the glaze on the cylinder walls and be sure to use cast iron rings. Chrome or other hard rings will not seat without a rebore. If you have 5# compression, your piston is still in one piece, but make sure you inspect the ring lands and clean the ring groves. You probably had stuck rings. I would fill the other 5 holes with something like Marvel mystery oil or better yet, you might consider pulling all 6 and putting on a set of cast iron rings. I have a grove cleaner, but you can use a broken ring ground square to scrape the carbon off.
