These holes for the studs are very close to the water jacket, so you need to be careful with drilling out the holes and installing inserts. I would try to find a longer stud and cut some threads a little furhter up on the stud so it grabs some good threads at the end of the hole. Heli-coil inserts can be installed with the head on if you have all the right tools. keeping your new hole straight and perpendicular to the head will be the challenge. There are some drill guides which can help you do that. A three fluted drill bit also helps keep itself on center. Spend some time researching on Youtube. Almost anything can be found!
