Others will confirm but to my knowledge there was not an 3 speed OD.
There was a 3 speed with 3 forward gear, and 3rd gear was non overdrive, or there was the 4 speed OD, available with 4 forward gears, the OD gear replaced 3rd, so the box is actually 1, 2, 4 OD.
OD is available cast iron, or alum housing, in long (B/E and truck) or A body configuration.