Mark II Fiberglass fins

I am searching for information on a most unusual aftermarket accessory offered back when our cars were new or very near new. Very strange, but someone was making and advertising a custom fiberglass tail fin panel that could be attached and fitted to a Mark II quarter panel. Kinda looked like a Chrysler tail fin, likely where they pulled the mold. I know for a fact these were advertised in some enthusiast magazines late 50s, early 60s. I recall seeing an ad and even a story on how they could be installed. Very rare but I'm serious, this is not a joke. Might sound horrific but amazingly they don't look as bad as they sound. Can anyone out there assist me in my search for information? Thank You.