The guide kink in each intake port sits below just offset from the recessed head bolt.
So when you grind too far, or purposely get into them....youll need to make a washer to jb weld into the head recess to fill the lil hole thats ends up kooking like an eyebrow yoy can see through.
The head on my 410 , j heads, have thise in the head bolt recesses when i went through the roof into the head bolt. Rtv, jb weld. As long as you use a hardened washer and rtc over and around the head bolt once torqued, youre good.