[jeffschevelle]

Z16's used the 3844100 pulley. They were cad plated with no stamped numbers or code.

66 and 67 Chevelle L78's also used the 3844100 pulley. They were cad plated, and some had the stamped number and AK code, while others did not. I speculate that there were two suppliers, and one of them die stamped theirs, while the other mfr. must have used a sticker or tag that got discarded at the assembly plant, or an ink stamp that faded away quickly.

The first silver one in your pics is a lot newer than the cars (based on the dot matrix printed number on the label), but it is a lot older than the gold one below it. The gold one is a much later replacement version.