Re: So let me get this straight.
Yes, I would find some "all thread" M6X1.0, and make a new stud, and JB Weld it in.
If you want to use the old one, clean the remaining threads with some type of evaporative solvent, and JB weld the stud in place. Let it sit overnight before torquing down.
8 lbs, should hold it it you torque everything evenly.
The worst that will happen is the head gasket may leak a little, but a lot of these engine do leak some.