I don't know, I haven't ever had a real 70 RM23 Superbird with an original, suggested retail price window sticker on it... I wonder if there is a different # after Superbird, if it's either a 440-6bbl or 426-2x4bbl Hemi, instead of the 440-4bbl.... There are some really knowledgeable Winged/Aero Car guys over @ Dodge Charger .com forum... there is also a Winged Warrior/National B-Body Owners Assn. @
www.wwnboa.org , you could try to ask over there or look maybe it up over @
www.superbirdclub.com/Index.html , for Daytona Superbird Auto Club & Talladega -Spoiler II Registry, serving the Aero Warrior community since 1975... I'm sure there are other places too... some kind of Nascar registry for Aero cars... they are a really tight nit elite group, some are also wound a little too tight...LOL... sorry I couldn't resist