For my two cents worth, go find a Truckstell overdrive made for dealer installation on 47-54 chev cars. it bolts onto a shortened torque tube. It should bolt right up to your tranny and mount to your tube. Truckstells give 28% overdrive,will change a 4.11 into a 2.96 or a 3.90 into 2.80. You'll still have your low ratios for "intown" and "parade" driving and a tall setup for the highway. They are a great unit if you can find one. Best Regards and happy motoring, KB aka telekenfun