Oldmanmopar, you have given me some good info that now has me puzzled. I have a 1971 340 Duster that was built on August 10, 1970, so it is one of the cars produced in the early part of the model year. It has a very nice sharktooth grille that has black horizontal fins. Looking at the back of the grille, it is indeed all gray.
I am a Chemist by trade and work for Boeing (formerly Douglas Aircraft). If you could send me one fin from the gray casting and one from the black casting, I would like to analyze them to verify that they are of different polymer stocks. Of course, the fins should come from any grille that is only good for parts since I don't expect and I wouldn't ask you to ruin a perfectly good grille. This would only help the discussion.
I, too, am 54 years old and I have dealt with many different materials in my career. In the aircraft industry, I have often analyzed plastic materials that have failed because a vendor substituted a cheaper material without our permission. It may be possible that Ma Mopar changed material for its sharktooths after 1971.
If you are willing to send me a sample of each type of fin, send me a PM and I will then send you a reply with my address. I am sure the fins could be sent via snail mail in an envelope for the price of a stamp.
Art
