If you have, one of the engine codes listed above it is an L48 which is the only small block motor SS's came with. The RPO Z27 is the SS package (L48 only I believe, not big blocks but I could be wrong on this.) The change from L48 to Z27 was a change in the way the option was listed by Chevy. I don't know if it was to make it similar to the RS (RPO Z22) and Z28, (RPO Z28). RPO L codes were engine codes and since the SS was more than just an engine package they may have wanted to change it to the Z codes which were special item codes. I do not know for sure that is why they changed it, that is just my best guess. Maybe someone with a little more knowledge about this than me will chime in.