My understanding is that you want a minimum of .025" clearance between the closest part of the cylinder and the head. One way to check the quench clearance is with solder. Insert it in the spark plug hole, and carefully turn the engine over through one complete revolution. Then measure the flattened part of the solder. That's your clearance. I use the narrower diameter rosin core electrical solder for this.

Good luck,
AV8TOR