That's a good question... personally, I just think it's a specially made convertible Z, and am glad they only built 1. I'll run for cover now with my popcorn and my gun...
I admitedly don't know much about how the '63 Z11's were built/ordered, but I'm guessing they'd fall into the category of Supercar pretty easily but I'm not sure...was the Z11 option an RPO? I guess if it was, they're not "Supercars" by definition, but are bad ass either way. The same can be said for many cars of the era.