no no no not on a head..most likely they will work there way out... if its stripped just make the hole 1 size bigger and re tap it then use the appropriate bolt
never want to do fixes like that on a major component do them the rightway..
first determain if it has enought meat meaning steel around the hole so it wont punch though the wall of the cylinder if you go up one size.. and check your head to make sure it wont go into the compression part when you drill the hole bigger for the bolt..
i had to put one helicoil in my case.head stud wasnt fully threaded into the case and stripped out, put in a metric helicoil and havent had a problem since. worked out perfect. helicoils work fine for stripped out head studs, just pull the stud out, drill the hole out with the drill bit from the kit, tap it, and insert the helicoil with red locktite.
And what do you mean steel? there is almost no steel in these motors. the cases, jugs, and heads are all aluminum.