Gibson customer service:
I am the original owner of my L6-S blond solid body guitar and love it!! Wouldn't trade or sell it for anything. The S/N is stamped in the back of the headstock between the tuning keys for D and G strings.
The 6 digit number stamped is 177778. I've looked on line and all I can figure out is that it was probably built in Kalamazoo, MI sometime between 1970-1975. It would be wonderful if I could get a bit more of a definitive answer from you all.
Thanks for the help with this S/N question,