i got this idea from roy @ roy's hotrod garage and it works great. Weld a bolt onto the broken bolt and turn it out. I had to do this on my door hinges. I managed to get 5 of 8 bolts this way, and they were VERY rusted. I think an engine bolt should be easier because it is generally dry.
"Well done is better than well said." - Benjamin Franklin (1706-1790)