This subject has been a mystery to me for a long time. I parted out a FC7 AAR back in 1983 that had the "fish gill" rocker trim on it. At that time I assumed that it was correct to the car. I saved the trim with the intention of installing it on my AAR, but I never got around to do so. Some years later I was told that the AAR's never had the rocker trim.

I just pulled out the copy of the broadcast sheet that I have for that FC7 AAR that I parted out. It does show the M27 code and no M25 code on it. I guess someone did add the fish gills to it early in its life.