What is this piece? Where can I find it

For a ‘64 Dart 225. I am looking for this banana shaped piece (circled in the diagram) that connects the lever for the downshift to the carb. Without it, when I go to floor it at speed, it does not downshift to increase acceleration like it’s supposed to. If I can get a parts number too that would be great. EDIT: Forgot to mention that's a carter single barrel carb

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