[tdw28210]

WHOOPS, Just read you already tried Norbet's site. Sorry.
Yes, some cars in the 84-85 range reportedly did not have the option tag on the underside of the hood.

Do your rear calipers hang off the BACK of the rear rotors? If yes, then you likely have a real M491. if not, then you'll probably have to open up the wallet. Let's hope you get positive news from Norbert or PNA. It is possible a PO pulled the turbo calipers and sold them off or even the entire trailing arm assembly and replaced them with narrow bodied arms. The latter is not likely because it would require changes to where the arms mount to the torsion tube.

The "special wishes" route is a long, tough road to figure out. I know of a car with pretty airtight documentation with regards to its factory widebody options that is completely ignored by the collector community. Good luck.

Let us know what you find out.