You can put a Cobra Jet engine and running gear in your car but unless your car has a Q or R (fifth digit in the vin) it will never be a true Cobra Jet car. The 69 had a 428 Cobra Jet engine. It had a big block 4 speed or a special C6 with extra clutches and a large servo and a 9" rear that had a nodular case axle carrier. There were two versions of the 428 CJ. The CJ and the Super CJ. The SCJ had 3:91 or 4:30 gears. It also had an external oil cooler, LeMans rods and different balancing. I'm sure I left some info out but somebody will probably add to it.