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The major differences between the 1980 and 1982 Daytona and the 1981 GTO are the hood, the tops of the rear fenders, and the rear spoiler/bumper cover. The Daytona had an elaborate, short vertical fin on top of the rear fender that turned several turns “in and back,” flowing to the wide, long, table-like rear spoiler. The GTO’s rear fenders pontoons are the same as.
The Zagato company took a C7 Corvette Z06 and transformed it into the IsoRivolta GTZ, a "spiritual descendant" of the Iso Grifo A3/C (Corsa).  The original A3/C race car was developed by Giotto Bizzarrini not long after he left Ferrari, where he had served as cheif engineer behind the 250 GTO, which is revered as the world's most expensive car.  Bizzarrini purportedly fancied the A3/C as his "own personal evolution of (and improvement upon) the GTO design."
The "Asteroid" started life as a 1963 Chevy Corvette.  It was ordered by mechanical engineer and renowned mid-century speed boat racer Bob Nordskog, sans any exterior paint save for a primer coat.  Instead, the car was shipped directed to Barris Kustoms with instructions for Barris to transform the brand-new Corvette into a more radical version of itself.
The Callaway C16 was Callaway’s 16th major automotive project. It was a limited production, bespoke automobile, built to order, by what the Press called “the best specialist engineers in the business”. These cars are seriously fast, beautiful, and exclusive. The C16 was a direct competitor for the Porsche GT3, the Lamborghini Murcielago, the Ferrari 599 GTB. It was both faster and more capable than its competitors, at less cost.