Why would these hard bolts break? Too much torque? Bottomed out in hole? Did you have any machining on the block to reduce metal depth? Did you torque in "steps"? About 1/3rd of torque, half, 3/4, and full? In pattern shown in book? I do know that modern small head bolts are to be replaced cause of "stretch" they go thru when torqued. I've never heard of this on older engines. Is it a cheapie import torque wrench and maybe it's not really setting at torque you have it set for? Something is fishy here, these bolts shouldn't have done that. Check your procedure and specs for next ones.
