If it is a true SS427 RPO Z-24, it would have the domed hood, SS427 grill emblem, special 427 numerals and side flags, SS427 trunk emblem, etc. Nowhere on the car will it say Super Sport except in the interior. The Super Sport emblems you speak of were used on the standard model of which you could get a 427 in. In other words, you could order an RPO code Z-24 optioned SS427 or you could order the regular Super Sport Impala with the 385 hp 427 engine. For a better explanation, go to
www.impalass427.com Some plants used a 4D code on the cowl tag but not all.
Rick