Well, this could be a tough one. If you really need the bolt to tighten the exhaust, then do you have room to drill out the broken stud with the head still on the engine. If not, and you really need it out, and since there is a broken extractor also in there, then remove the head, yes I know more work and a lot of bad words, and work the head on the bench. Use a torch to heat up the area, and you will find it will just slide out, with a little work. Check valve seals after if you use heat.