I am willing to bet that if Gibbs told the factory to make one or two RS Convertibles of his 50 Camaro ZL1 order, they would have. It would have made no difference to them as its not really any extra work. Just pull up a 12467 body and drop in the ZL1 stuff. As long as Mr. Gibbs was moving large amounts of product, was a good franchise customer, and paid his invoices, I think it could have been done. Back then an owner of a dealer could call up GM and if he knew the right people, could get it done. The fact that Gibbs was even able to get them to build the ZL1 to begin with proves that you could move mountains if you had the money and the influence back then. I may be wrong, but if you look at the 67-69 Camaros, there seems to be a lot of exceptions to the rules that shows that special things could be and were done if someone was willing to pay and knew the process.
You can't use the argument that it won't happen today, therefore it couldn't have been done in 1969. If a bigshot Chevy dealer tried to get GM to build 50 ZL1 Camaros today, it just plain wouldn't happen. I believe that ordering a Camaro today is very different than in 1969.
Again, just my opinion...I may be wrong. Of course, there is no way to prove this since my current attempts at building a time machine have failed. In fact, I suppose I should just stop trying to build one now since if I was successful, the first thing I would do is visit myself and show me how to build one. Since I have not seen myself from the future I guess I never figured it out. Or maybe I have to figure it out first and then I will get a visit from myself. OUCH...my head hurts.