According to this Western Union Telegram dated June 1, 1967, the founder, president, and chairman of the National Hot Rod Association (NHRA) Wally Parks asked Chevrolet to provide six 1967 Camaro RS/SS convertible Indy Pace Car replicas for use prior to, during and after the 1967 NHRA drag racing event known as the Springnationals held at the Bristol International Dragway in Bristol, Tennessee June 8-11, 1967. Notice that he wanted everything on the original door decal to stay the same with the exception of replacing the Indy 500 information with the Springnationals information. Ultimately, it looks like the request was never fulfilled. The cursive writing on the telegram states that "wire sent to NHRA - turned down." I'm not sure why it was turned down but asking for these cars only five days before they needed to be at the event might have had something to do with it. That seems like too short of a lead time. Please share if anyone knows why.
I found this document in the 1967 Indy 500 Pace Car section of the Pilot Prototype Registry web site:
http://www.pilotcarregistry.com/1967-pace-car-documents.html