Rancho Jeep Supply (Later to be known as Rancho Suspension) developed an aluminum alloy adapter for use with a Borg-Warner overdrive that would mate up with the Bronco's Dana 20 transfer-case. Model B-100. The picture to the right shows the output housing that is removed from the transfer-case and the overdrive unit that is put in its place. As evident in the picture the rear drive must be shortened 9" to use the overdrive.
An article covering the "New Overdrive" appeared in the October 1968 Four Wheeler magazine, pg. 22-25. (Thanks to Todd Z. for supplying the article) The article gave credit to Clarence Shook and Basil "Smitty" Smith as the team that created the Bronco overdrive. Ken Roggy Ford of La Puente California was originally selected as the "Exclusive" distributorship of the B-100. The article went on to mention that since the Bronco has power to spare (V8) that the overdrive would make full use of the power giving increased fuel economy and performance. The following is the results of their testing:
MPH OVERDRIVE (RPM) W/O OVERDRIVE (RPM) 35 1200 3100 65 2600 3900 70 2900 LOUD Gas mileage increased 27 percent (17.5 vs 13.7)