I am building my next motor. It' a '76 455 and I found something unusual or maybe not so. I found that between the 4-6 and the 3-5 cylinders, the coolant passages were closed. They appeared to have been overlooked. I tapped on them and they felt solid. But I took a small punch and lightly tapped, made holes in them. I opened them up and was amazed that the casting that blocked the holes was never caught at the factory and that the engine lived it's whole life like that! It went off the road in 2015. It reminded of the last engine I did (also a '76), the bottom passenger side bellhousing bolt hole was never tapped! I guess the line worker couldn't get the bolt in and just tossed it to go to the next car!
If you could "lightly tap" with a "small punch" and you opened-up holes in the block's deck surfaces, I have to think you weren't tapping on cast iron, you were tapping on rust deposits or something similar. How big are the holes in the gasket that cover your new holes in the deck surfaces? Photos?
John, have a look at these threads. http://www.v8buick.com/index.php?threads/455-cooling-port-casting-blockages.308541/#post-2564206 http://www.v8buick.com/index.php?threads/400-430-head-gaskets.303718/#post-2517909
The metal was solid across. I had to use a die grinder and found the casting was thick as a nickel. The holes now match my felpro "professional " gaskets.
