Here's some more info on the 2255. It was built on May 13th, 1974. It has the shorter 2 wheel drive pinion shaft. It is coded as a diesel with wide front, but they were all diesel, with either wide front or front wheel assist.

I haven't done as much research on the 1955, but here's what I can tell you. It is diesel (only option), adjustable wide front axle, (believe it or not, narrow front was an option for the 1955). It too has the short bevel pinion shaft, with 7 teeth on the pinion and 41 teeth on the differential.

According to my serial number book, it is a 1973 model year.