Try a longer bolt, if there are threads at the bottom that grab the bolt take a nut , thread it on the bolt, take a hacksaw and almost cut through, tighten the bolt and the head will twist off, making a stud.
Actually once installed the bolt is not needed, I only resurfaced the exhaust manifold and have a little gap, NJ only has ethonal gasoline and the cooler intake manifold seems to help, my bolts are just tight enough to compress the lock washers slightly