You did realize that the '75-'78 Iron cased A body and F body V-8 trannies aren't overdrives, right? No, not the /6 iron cased ones, V-8.
They use a 3.09 low gear with a direct drive 4th gear.
Pretty rare piece and the tip off as to it being a D.D. V-8 tranny is the bearing retainer LOOKS like an O/D bearing retainer, but has the bolt spread of the older 4 speeds.
Much like the '73-up 3 speeds in vans and trucks.
This is similar to the difference in bearing reatainers from a '69 B body 383 4 speed as opposed to a '70 B body 383 4 speed, same bearing retainer diameter, but different bolt spacing on the retainer.