I stripped the bolt heads. Threads in the block are all ok. I am slowly convinced that 12-point bolts are the way to go. I will put the new goetze ones I have into the block without the head and see how much thread is in there. I suspect the block has some extra thread to accommodate for when parting surfaces of the block and head need refacing. I like the idea of thicker washers. The fsm says that the newer washers are hardened so I would have to find out what the hardness is if it turns out I have to buy hardness-equivalent thicker ones.