AGH! I had some broken bolts in my 317 heads and was able to extract them. I hate extractors and gadgets that only break off on the hole you drilled and make it even harder to get them out. I drilled a small hole in them very carefully making it very straight. I pounded a hex wrench into the hole. I did my best to heat the surrounding area of the head and the bolts came right out. Pounding the hex key in does two things. It "shocks" the threads and provides a means of attachment to the bolt. I used a very high quality hex key so it would not break. It was the first time I tried this method and the first time I did not have to pay a machinist. Go to post 21 here
https://67-72chevytrucks.com/vboard/...d.php?t=808928