1969 was the benchmark year for Ford Mustang in its proliferation of performance names and engines. No less than 6 factory performance Mustang models were available (GT, Boss 302, Boss 429, Shelby GT350, Shelby GT500 and the Mach 1). Additionally, seven variations of V-8s were available in the '69–'70 models; most of these also available in the new Mach 1.
The Super Cobra Jet (SCJ) included the big 428 V8 and a "traction lok" rear axle with a 3.91 or 4.30 ratio as the "drag pack" option.
Source: Wikipedia (original)