OK, so digging further, I remembered about Bob Perkins 3800 mile 1966 K-Code automatic Fastback. I remembered there was a bunch of pictures in the article (
http://www.mustangandfords.com/featured-vehicles/mump-1005-1966-ford-mustang-fastback/).
See attached picture of his trunk and spare tire with SS wheel. Notice the wing nut and j-hook. Now we know he did some work on this specific car, a sort of "refresh"... so I wonder if he replaced it or if that's original. To me it looks like the j-hook is pretty long sticking out from the wing nut, and notice the wing nut itself, it's more like the style of the additional attachment of the "NOS" wing nuts that I found a picture of.
Also for fun, notice he has the correct smaller plate for the SS wheel, but it's upside down, the tabs are supposed to point down into center hole of the spare aren't they?
So the question is, is this one of those parts he "refreshed" or is it original to a 66 car with a SS wheel spare...
Thanks,
Jason