The correct way to clean the piston tops is by scraping off the carbon. Don't do this with anything like a chisel or screwdriver that has sharp corners. In fact a piece of hardwood would be better to ensure that you do not scratch any grooves into the piston tops. Any scratch or gouge will provide a place for a crack to begin.
Once the pistons are out, since the tops are already cleaned, just clean them well in solvent, and then break an old ring and use it as a scraper to carefully scrape the carbon out of the ring grooves before installing your new rings.
Goetz makes good replacement piston rings.