I second bakat's method. Even though the original broke, it may turn out fairly easy. Try rorating it out with a punch, as you would remove the headless bolts of the steering lock. Takes a long time but might come right out.

A10 and A12 Head Bolts are interchangeable. B110 bolts are stronger than B10 bolts. The '13' bolts are the last revision and are even stronger. The center bolt differs between early and late blocks.