Be interesting to know any tag or casting numbers on that. It is a 3 speed with over drive, but what I see in the pictures says to me it has an early top loader tail housing on it. My experience with the od trans is the rear output bearing is larger, so that tail hosing had to be opened up a bit. That tail housing has Mustang shifter bolts drilled but also has Falcon bolt bosses not drilled. Hard to find that tail housing when you need one.
I used to use those overdrive trans in early Bronco's because it has the 3.27 first and the od 4th.