[15max]

Thanks for all the kind responses. I tried the vise grips, bent wrench and several wedges with no success. Finally I made this plate to fit the head. It required a spacer to hold it against the bolt and even a large C-clamp to keep it tight. However, the nuts still would not budge until they were heated as mentioned by Gary.
One more ordeal. It certainly was satisfying when they came loose.