That my friend is a casting flaw. I have seen plenty like that and worse. I have seen one where the right side rear bore aside of the distributor was mostly gone. We had to spray weld it and bush the bores. It was an X block. You can just barely see the weld and the heat mark where it was done. Yours is not a problem at all. I'll bet that block you have is a high casting number. They always are. This one was a 318-11
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