1965 273 Head Gasket Question

Great result. How much were the Cometic head gaskets? I also wonder about oversized cylinder holes. I've wondered if the gap just fills up with carbon so no compression is lost. That would well-protect the steel fire-ring. The head gaskets in my 1982 Dodge Aires 2.5L were notorious for failing before 100K miles, attributed by some to the fire ring getting squashed slightly into the combustion chamber.

I suspect those coolant cavities are supposed to be blocked off, though perhaps OK if the gasket exposes them. They are likely for shaking out the sand after casting. Most likely those cavities are connected to the rest of the coolant by openings around the cylinders, but I don't know the block design (does anyone? might have to look at the cores used in casting or cut thru a block). Whatever you do, don't get the bright idea to add holes there. I did so years ago when a dumb kid on my 1969 slant-six. I thought "WTF, needs a passageway, gasket must not be for my year", so drilled a 1/2" hole (front of engine as I recall). Started the engine and it began overheating at idle so shut it down. I then lifted the head w/ intake and exhaust manifolds on up about 4", slid that gasket out and a new one in. Since new, the engine surfaces were still clean and didn't need anything but a little razor blade clean-up. BTW, later read that 2.5L owners would do that trick to quickly fix their routine gasket failures. I can't say that my bright-idea hole caused the overheat, since could have just been from trapped air which could have corrected once purged.