need posi de-code

[Brian376]

I recently acuired a 10 bolt posi and wonder if you guys can help me figure out if it is a 3-series 8.5inch. The numbers on it are "410409 N" and under those are "GM 7" . Also, without the ring gear on it, the outside diameter of the "ring gear mounting flange"(I made that name up) measures 7.5"

Thanks for any help!
Brian

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79 Z28 with a few mods