There's a dealer here who has one and claims that it is "1 of 12" so I called and asked what documentation they had. I caught him off guard and I'm pretty sure he really has no idea other than what the previous owner told him. It's a 4-speed car and he said the 4-speed cars are really rare, but I'd be willing to bet that a third of SS427s were sticks. At least through 1967, most hi-po cars were sticks till the advent of TH400.
There's another one in the area as well, so does that make it 2 of 12?