There are many early 68s that have the double stamp. IMHO some PO found some GTCS parts and made a beautiful car with them. There are a lot of Shelby clones out there and I take it as a complement. What is wrong is to sell it as a real Shelby.
A real clue to the clone thought is if it has original fiberglass. If it is all aftermarket fiberglass, the clone thought always applies. The availability of original fiberglass today is scarce to almost unobtainable. Certainly, a piece here, and real grill there, but it would take some time to collect it. The rear taillight wiring harness. Can't remember if Neil looked at that? There is also a possibility of a wrecked GT/CS long ago. That would allow for the collection of a lot of parts to build a GT/CS clone. One thing that tempers this is most wrecks are either rear end or front end. There goes some of the parts. But certainly, a possibility.
This car is so out of the realm of the production it should be questioned. And if to be considered it should be thoroughly inspected on a hoist by the best of the best. Possibly even disassembled a bit. I had to perform this on a 1968 427 Cougar GTE that was red flagged by the Cougar GTE experts, but it turned out to be the real deal.
Neil did not have enough time to really look it over and until such time it should not be included in the current registry until inspected.
Rob