Bitter based his original CD designs on those of Frua, before making alterations closer to production. The basic design changes to Frua's CD design vis-à-vis the 1969 Opel CD consisted of a truncated rear end, modified windshield and less chrome application. Dave Holls and Opel's design team supplemented the design with a small front spoiler, larger grille, higher bumper bars and by prolonging upwards the lower edge of the rear side windows across the C pillar to the rear hatch. Final prototype testing was conducted at the Opel Test Facility in Duden, in addition to load duration tests by Bitter at the Hydropulseur facility of Baur.