With the availability of "budget" tools available easily from outfits such as amazon, a decent dial bore gauge should be in every hobbyist engine builders tool box. The FIRST thing you do is measure for taper, AND out of round. That will tell you if your re-ring project can be successful. You do NOT check rings with a flashlight, and you damn sure dont check bores with a carpenter's level like has been suggested by your youtube hack. There is more knowledge and skill on this site ready to offer free advice and help than anywhere else.