GM uses letter codes for their class/chassis platforms that were used by all divisions. The full size Pontiacs were known as “B” bodies, the mid size Pontiacs of the era were known as “intermediates” or “A” bodies, the Firebirds were “F” bodies, the smaller Ventura II that came out in ’72 was an “X” body, Grand Prix was a “B” through 1968. When the smaller GP came out in 1969 on a stretched “A” chassis, it was redesignated a “G” body.