FordFarmer is correct on 1H31B being the production code, meaning that he tractor left the assembly line on August 31, 1981 during the day shift, and that the C at the beginning of the serial number means that it was made at the US plant. The rest of the serial number does agree with the production code in that it's a 1981 serial number.
CA212? is the beginning of the model number. The CA2 at the beginning means it's a general purpose ag chassis 3600 made after some date. The documentation that I have says that they used CA1 for the 3600 models when they started producing them in 1975 and by the end of the run in 1981 they had switched to CA2, but I don't have anything that says when they switched. The 1 means that it has a diesel engine and the last 2 means that it has a trans driven PTO. The last character, which is missing, should be a letter, and would tell you what type of transmission it has, which could be a 6 speed or an 8 speed or a 6x4 manual reversing trans.
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