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I think that was unique to Chevrolet 1965-1969 carburetors (maybe just small block?). I believe it was added to address mixture distribution on the "high" side of the dual plane manifold. Maybe others can provide more info.
This QJ is off of an 86 Dodge truck. I have 2 of them that are identical - 17085408.I think I saw someone say it was a stop for the air door somewhere, but I made the door adjustable and it doesn't contact it even when fully open.