Were 428 Super Cobra Jets only available in 1969 and 1970?

The 428 Super Cobra Jet engine was first available in 1969, exclusively available when ordering either of the optional 3.91:1 or 4.30:1 rear end gear ratios. The Super Cobra Jet included a number of reciprocating assembly changes to stand up to the rigors of drag racing, including beefy capscrew connecting rods, cast pistons, and a crankshaft, flywheel or flexplate, and harmonic balancer distinct from the standard 428 Cobra Jet. An external engine oil cooler mounted in place of the driver's side horn (the horn gets relocated to the passenger side) and the distinct balancer with counterweight are the only visible clues to what lies within.