Tractor Repair: Year identification, old ford tractors, industrial models

Question
I recently bought a Ford 3550 tractor/loader at an estate auction. Although it runs pretty good I want to change all the filters and get repair manual. I've been told the ID should be on a stamped aluminum plate but I can't find one. Numbers stamped into the right clutch housing are D2NN 7006 D, on the left housing there is C5NN 40240 Y and above this number is stamped N25 5 74.  On the right lower engine block is D4NN 6015F. Will any of these numbers give me the year of manufacture?

Answer
Hello,

  Don't know if these industrial models are different, but the ag models always had a metal tag under the hood.  If you flip up both sides of the hood and look underneath, there should be a data plate with lots of numbers.  Look for a unit number on this plate.  The unit number will tell the date of manufacture.  There will be a number, a letter, another number, and another letter, which in my experience is always a B.  This combination  means the year, the month, and the day.  For example, a unit number of 9A21B means the 9 is the last digit of the year, A would mean January, 21 is the day of the month.  Not sure about the last letter.  I was told this is what shift at the factory built it, but like I said, all the ones I have seen have always been B, so I don't know if whoever told me this knew what they were talking about or not.  If this does not help, I know someone that I can ask that specializes in old Ford tractors.

                Good luck,

                  Arnie