Keith L, others,
To add to what Craig said, the front spindles changed from the pin on collars to the bolt and washer at S/N 10,333, and to my knowledge that is the only change that the parts manuals give a S/N break for. It was thought the front axle casting was changed from the thin to the thick casting at about the same time, however a TC-82, parts manual, Revision 6 dated 2-64, shows the part number for the front axle as 376 140 R1. The "R1" would seem to indicate the axle had not been changed or revised, but we know that is not true, just don't know when. It is thought the slot in the frame for the creeper handle was around the 11K S/N range, and the same parts manual only shows one P/N for the battery hold down, and it is the "angle iron" type rather than the wire type. So, unless more information, such as service bulletins that tell of a change, comes to lite, other than the spindle collars, everything is just a guess as to when things changed. It is generally agreed that an Original with an un-slotted dash pedestal, no creeper hole, spindles with collars and a thin axle, is an early tractor and usually found with a S/N from the first year of production, and usually from the first half of the year, but not always. Parts are easy to change, and they did break - thin axle for one, pedestal damage from battery acid, etc, so unless you have a complete history on a given tractor, it is hard to be certain 45 or so years later, what was or was not on it when it was built, but comparing the S/N and the features with others of the same range should give you a pretty good idea.