I got to considering why so many heads suffer from these awkward to repair cracks to the threads securing the 4 central rocker box bolts.
I thought these bolts were all BSF, like the cylinder head bolts. But no, early ones are Cycle, later ones are indeed BSF and so forcing the wrong bolt down the hole is a possible reason for the damage and cracks. You can bet the head you have is the one on the change or someone used the wrong bolts.
So there you are, check the thread type on any unknown head and basket case bolts before reaching for the breaker bar. They should be a nice free running fit into the head.....and nip up easily. As usual with a blind hole, clean out the crap and check the bolt does not bottom out.
Today there are new repro's of the different types on ebay so if you're in the market for new ones check that thread type. The head you have may not be contemporary with the original model year so choose the thread that fits, not what the book says. I'd also add that if you do buy new its worth making sure they sent the right ones if you find "That thread's a bit tight"
Swarfy.