Slide the intake off the head. That will expose the stub of the bolt and you may have enough room to use a bolt extractor. If there is not enough to use an extractor, then put a nut over the broken bolt and weld the two together. Then you can use a socket to remove the broken bolt. The heat makes it come out easier. If it is flush with the head then use a washerand a nut and weld the nut to the stud. The washer keeps it from ruining the head as you weld.

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Paul
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retired mechanic after 35 years
specialized in Holley carbs and Ford Automatic Transmissions