Try looking for a 60-66 truck rearend first. They did come with 3:36 and I believe 3:08 gears and should be the right width, double check before spending any money, though.
The 3spd OD has a solinoid and a govenor sticking out the side of the tailshaft housing. Take a look at a factory shop manual from about 56-62 car or truck for details on the tranny.
