I'm betting you don't have a lot of room. Otherwise I'd say try to stand a washer up and weld it to the broken bolt if possible. The heat will help loosen it and then you can twist it out.
I once seen a guy put a nut "over the twisted off bolt" and fill/weld it up and then twisted the broken stud out.
I have also heard some guys say Speed Outs work and I even have a new set of them (Christmas present) but I have not tried them. They screw in backwards hoping to get the stud out.
...or if you have room, you can try drill from a small bit to a little bigger...bigger...bigger, until the "shell" will screw out. But, you have to be dang near perfect with center punching it to do a good job. Then you still may booger up a hole and have to use a heli-coil. Worst scenario would be to pull the head and have a machine shop take them out. Ugh!
I'm just a novice with lots of idea's but maybe the pro's will be by in a little with a simpler solution. I'm waiting to!!
