[Daves55Sedan]

You have a typical small-case two speed Ford-O-Matic. They were commonly used for Ford full-sized cars V8 and 6-cyl applications beginning in 1951.
The 1951 thru 1954 Ford-O-Matic's had a cast-iron rear extension housing. From '55 on up, they had an aluminum rear extension housing.
'51 thru '56 had air-cooled converters. '57 and later (with V8) had water-cooled converters, but they kept the air-cooled converters for the 223 I-6 all the way thru to '64 I think (when the 223 was discontinued).
If I remember right, the Cruise-O-Matic had a slightly longer case (known as the medium case). The transmission fluid pan was shaped a little differently and had a little bumpout on the passenger side. That has always been the easiest way for me to determine the difference.
The Cruise-O was normally not used on full-sized cars, but they were installed in Mercury cars and wagons and they were installed in Ford Thunderbird's. I just don't know what year they started. The '55 T-bird came from the factory with a 292 as the 312 was still a year out yet.
Lincoln had a whole nuther animal, known as the large case Ford-O, and if you saw one of those, you could easily tell the difference without measuring.