hi gentlemen , just went through the same thing on a 7.3 diesel, two bolts broke off flush with the head. had to drill them out. my question is on one of the holes I used a slight to big of bit!!! after retapping, the bolt is a little loose, have about half of the thread depth it should have. can I go to the next size tap and recut and use a 7/16 bolt instead of the 3/8 ??? the holes in the manifold will allow the larger bolt. (cast iron heads)