Need some info on what this manifold is from?

Cruze426 said

Not going to argue when it was cast, but it would have been on a '71 or newer Thermoquad engine.

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No it's not. While technically it is a spread bore intake as per definition, it's not the thermoquad pattern. It's for the Carter AVS that did have smaller primaries then secondaries, just not as exaggerated as the thermoquad.