Ford has a numbering system that gives the year, where it was made, part number and shift it was made on. Started the number system at the start of the 60's.
C is 1960's
3 is 1963
TR is where it's made or cast. (Not sure in this case, would have to look it up)
3550 is the part #
A is the shift it built. A morning, B afternoon, C evening
The DIF I don't know, could just about be anything.
A 1961 steering box may have C0 or C1, depends how far ahead of the production run it was built. Cool thing is, you can get the general vintage of the part by the first two digits of the prefix of just about any Ford part made, wether truck, car, tractor, or agricultural equipment. Worked at a Ford tractor dealership for a few years in the early 70's and learned about this back then. Kind of forgot about it until this post. Don't know what they did for 2000 and on, never thought about it. So much for trivia.
