Hubcap ID please

Good evening folks. What I have tonight is a set of Plymouth caps that are in really nice shape, the belong to a friend and we wonder what they were originally for. Best I can determine from looking at ebay might be '66-'67 C body. There are two numbers on them: 2660991 & 552006
They are very heavy!
C

PS - also a value range, my friend does not need/want them.

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