Seeing a lot of exhaust bolts stripping out the head. Customers would drill and put in a Heli-coil (which I'm not a fan of), or drill it out to the next size and try to thread it. How I fix is to drill out the bolt holes to 3/8". I machine a piece of aluminum round stock to fit the hole. I champfer the hole with a counter sink. I insert the plug with some aluminum epoxy into the hole. Let it dry and weld up the plug and dress it off.. I use a header flange as a template and mark the hole with a transfer punch and drill and tap the hole. I bolt the flange down and using a transfer punch, I mark the second hole and drill and tap it. I insert studs and use tall coupler nuts that I drill for safety wire. Head saved.