About 5 yrs a o or so, I took my SB cuda out in the early spring. While (ahem) blowing the carbon out of the engine, there was a funny noise and I started to see steam escaping from under the hood. Luckily I wasn't very far from home so I got it back in the garage w/o ia problem. Turns out the last header bolt on the driver side head had blown out. Since it was under the brake MC and right by the steering coumn, there was limited access. I took the opportunity to remove the heads and take a look inside the engine. Something I wanted to do anyway cause you never know what you have on an old car unless you did it yourself or can trust the previous owner. Anyway the outermost holes for the exhaust manifold/header go into the water passages and the threads in the hole that blew out were completely gone. So I heli-coiled it with no problem and it's been fine ever since.
But I DID install studs in all 4 outer holes, sealed them, and bought stainless nuts to use in those locations. My whole point is there is minimal usable thread length available there because the hole goes through a somewhat thin wall into a hollow cavity. And it's not an ideal situation to keep screwing and unscrewing screws into such a fragile tapped hole especially because you are liable to get cooling leaks as it wears. Just one extra tug on the wrench could easily strip it out.
