the fronts are 3 1/2" and the backs are 11" wide. Mine have the 5 ear caps that are held on with screws. Probably from the late 60s or early 70s? Let me know if you want a picture of the shelby caps or something I could dig them out.
With those widths I'd assume they were sold aftermarket. It sounds as though the center caps are a different design. According to the photo Anders posted, his push in instead of bolting on. I Googled images of Cal 500 Shelby wheels on saw a few different variations.