good luck on the drilling of the rest of the bolt hole, i would not rust the hole repair stuff on a head bolt , it works great on parts that do not have a lot of stress on them , it is a mix of powered metal and high grade epoxy, take alook at their matrix chart and for the size of the head bolt , it doesn,t appear to have enough strength to trust for a long period , not counting the amount of work to repair if it doesn,t hold, if worst comes to worst let me know later i have 12-15 of those blocks on hand most all of the time that could be rebuilt , JERRY