You are correct. The Z27 DID NOT appear on the 1970 SS cars that were built in Norwood. Only the L34 & L78 BB codes were on the trim tags. As I'm sure you know, the Van Nuys cars had nothing at all to indicate what the car was. I have had several 71's, and they did have the Z27 SS code, for both SB & BB cars. The SS-396's aslo had the LS-3 code.
