I have a 75 or 76 /6 and an earlier super-six manifold. I notice there is an extra manifold stud and opening at the back of the cylinder head manifold mounting surface. What is that and do I need to cover it/ bolt on some new part?

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/6 '67 Barracuda convertible, electronic ignition, 4-OD, street cam, SBP KH discs, 3.55 SG 7.25" 1" t-bars. Bilstein.
340 '67 fastback, Doug Nash 5-speed.
1988 Toyota pickup work truck

The opening is about an inch in diameter.

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/6 '67 Barracuda convertible, electronic ignition, 4-OD, street cam, SBP KH discs, 3.55 SG 7.25" 1" t-bars. Bilstein.
340 '67 fastback, Doug Nash 5-speed.
1988 Toyota pickup work truck

pipe plug

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Yeah....Im the one who destroyed this rare, vintage automobile.....

That sounds like the opening for the air injection passages. You can probably tap it and put a pipe plug in it, but I made a block-off plate and bolted that over it instead, with a stock gasket. We'll see how well that approach works in a few months. I imagine plenty of folks have done it that way before, though.

That's the air injection port you're seeing. There's a factory blockoff plate available for it, P/N 3751 249, and gasket 4275 834 (though the gasket comes with any decent-quality manifold gasket set).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I just used a small "freeze out" plug, but I have no back pressure. I am running open headers.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225