833 to 833OD

There are, in truth, 4 OVERDRIVE main cases, 2 of cast iron and 2 of aluminum, ALL are available in either the A/F configuration OR the truck/van configuration.

The there is the earlier, pre-'75 versions.

The guts will swap between either the 4 speed case or the overdrive case(s), whether it's the early, small input bearing variety or the later large input bearing variety.
The main difference is that the cluster is FLOATING (and requires a welch plug to seal the front end) on the later ('75-up) cases, rather than pressed in as on the early cases.

The other difference is the style of reverse ball detent, which is why there are 4 Overdrive cases.
The later case has the ball-spring detent in a small hole (@ 1/4") drilled into the sidecover mounting flange, the early(er) case (pre-'77) has the ball detent behind a plug on the driver's side rear of the case.
Yes, there are TWO styles of LATE cases, with regards to the reverse detents!!

There's more, LOTS more, but that's yet another book of it's own. :D

Mark.