My '73 CJ5 with a high torque (modified) 258 engine is great, but with the 33" tires and 4.56 gears in the back it makes my top speed around 60mph... What are my options for adding overdrive to this???? I know that warn and others made overdrive units, but I beleive that they are only for the Dana 18 (mine had a 20). The switch out from D-20 to D-18 involves a new Rear Axle housing if I remember correctly. Has anybody attempted putting a 5 speed in a CJ5???? And if so with what luck?