I was adjusting my rockers on a 67 327 engine. When one of the bolts wouldn't turn either way, broke off. How do you remove the stump to make way for the new one? Are these pressed in? There is no nut at the base of it so it isn't threaded into the head. Anyone have any useful experience with this sort of procedure? I would appreciate some input since I am a bodyman more than a mechanic.