^^^^^^This...and you need to know how far out of the deck the piston is. OE was .017-.018 depending on whose literature you read.
If you have 65 cc heads and if the piston is out of the hole you’ll need to figure out what the CR is. If you are willing to do the work you can be 10:1 on pump gas fairly easily.
If they are OE heads, it’s likely they aren’t that small, which is ok too because if you end up at 9.5:1 is there is nothing wrong with that either.
But you MUST measure to know. Guessing at CR has made engines that should run hard run like a wounded hog with no legs, so don’t guess on your CR.
