They were built by Hurst. The SS/A option meant a lot of the interior was not installed by the factory, seats changed, fiberglass fenders and hood and some other things I am not too sure on. The car was then sent over to Hurst to be finished with Mopar Performance spring locators, a Hemi K-frame and of course a 426 Hemi. After they were finished they were shipped to a dealer and sold as a car that was 'recommended for sanctioned acceleration contests only and not for street use'.
You could also get a 440 in the same package, but apparently they were not nearly as popular as the Hemi.