Further to Julian's comment; it's likely your ZF's case was replaced at some point in its life with an M1 case. Years ago, the M1 case was a Hall Pantera catalog item. The ZF's redesign took place during the development of the BMW M1, which was first sold in 1978. I have an M1 ZF in my Pantera but my serial number is about 7,000 higher than yours.
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