AMT brought out a 1/25 promo model '67 fastback (in 1966), then produced it as a kit. They modified the molds to a '68, then to a '68 Shelby. The Shelby version was still available as recently as a couple of years ago, but the various mold revisions have made the stock versions, particularly the '67s, extremely rare.
Around 1994, AMT cut a new tool of the '67 (still a fastback, but a very nice kit, BTW). They re-released it with additional parts to make a '67 Shelby and, as far as I know, the molds for both versions are still in existance. Kits pop up on e-Bay from time to time. There was rumor of a California Special version in the works, but I've never seen one myself.
Visually, the '67 had "cheese grater" grilles at the rear quarter panel scoops, where the '68 had a simple "C" molding. Gas cap, hub caps, front grille and interior trim details varied between years and specific models. All "California Special" models were based on the coupe, and used Shelby-inspired tail lights and rear spoiler.
Phil - former Mustang affecionado