I highly recommend the overdrive option if it is the original type Borg-Warner with freewheeling clutch. I replaced my 3 speed with this unit on my 57. It bolts right up. Furthermore the original set-up with the kickdown linkage can be greatly simplified by simply wiring the OD solenoid to a dash mounted switch. The OD can then be activated whenever needed. It's a simple and easy solution that reduces my 3.90 rear to effectively a 2.61. Compare that to the commonly available 3.36 ratio rear end set advertised for these trucks ($400, ouch!) If you have any questions, contact me and I'll be happy to help.
