trying to decode my 69 rs z28

[Unreal]

Without paperwork, or original driveline, it's nearly impossible to prove it's a real Z/28. You will have to rely on detective work to "deduce" its origin. Do a search here, and Team Camaro (Camaros.net) to get a list of clues. BU rear is a start, as that was the standard rear on the Z. Of course, it was available on other models, too.