From looking through the parts books it looks like the '67 383 4bbl., for Plymouth, uses the dual snorkel air cleaner with the round snorkels(the same part number as a '66 383 4bbl., and I think they all used round snorkels in '66). The '67 440 used a different air cleaner with a "newer" part number, so I would guess that those were the oval snorkel.
There is even an air cleaner listed with no snorkels. I have no idea what that one would look like.
Any of them would look good on the car, and a hell of a lot better than what is on there now.
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