I think the can shell of the 137s was initially black for 69-71 but switched to just being gold zinc by 72. Note that the bottom base part with the threads was gold zinc for all. The 137s were also used on Olds. In 73 the number was changed to 6463727 and these were all gold zinc. The earlier acorn ones I have seen have all been gold.
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1968 Firebird 400HO convertible
1971 Trans Am 4-speed, white/blue
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