Breaking two bolts in the same hole is one too many, without finding out what's causing the problem. Maybe there's an obstruction in the bottom of the hole that's allowing the bolt to bottom out, or something similar. I'd suggest installing a Heli-Coil in that thread, and making sure that the hole is deep enough to let the bolt squeeze the head gasket properly. The best fix would be to install ARP studs in all the holes,instead of using 70 year old bolts. That's what we did on 1,000+ HP tractor pull engines.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!