There's only two rubber stoppers I can think of in the rear axle well of a 67'.
One is the pair of somewhat triangular shaped rubber stoppers directly above the axle on each side that prevents the axle from smashing into the frame in case the axle moves all the way to the top of it's travel (mitigates the damage from the axle on the frame when it bottoms out).
The other one is on a bracket mounted to the inside of the frame rail behind the axle, and it was to hold the muffler on the 6cyl versions.
Either of those sound like answers to your question?
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