1965 273 4-bbl intake. What is this connector for?

RustyRatRod said

That casting goes ALL the way through the intake. I wonder if they put it there for an optional PCV or crankcase breather?

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Just a bulb shape on the bottom side. It doesn't feed into the runners. In 66 the CAP (first year) was a hose from the air cleaner to a vented oil cap.