Welcome John!
You sure dropped a bomb here with this information. Nobody here has heard of a Hertz "68 GT/CS" and believe me, Paul N. and the other members here are the last word on these, and this is a surprise to everyone. What color were these cars? Any information or history available on it, where these 50 models went, what equipment they came with, and what equipment they came with?
I doubt Hertz would help, because I called Hertz car control once about a Buick Skylark I was seeking information on, and they said (quote) "We have that information, but we will not give it to you"
I am sure Paul N. would appreciate any documentation you could share about this, as he is writing a second edition of his book on the California Special, and this is worthy of mention. Do let us know more here, thanks, and again, welcome!!!
Jim B