You're done. Look for new heads.
The new Mex 043 heads use 3/4" long plugs instead of 1/2" for this very reason. More meat means less chance of cracks. CB 044 heads also use long reach plugs, and they go with smaller M12 motorcycle plugs, again, to prevent this.
If you're thinking of 10:1 CR, you will need the benefits of long reach plugs.