If you are trying to sell it, tell where (well, at least approximately) you are, and WHAT you are selling. A 51 Kaiser covers a lot of territory. Kaiser or Henry J? Colour(s), interior and exterior, including material on the inside; automatic, standard, standard with overdrive; Special or Deluxe; 2 door, 4 door, or Traveler utility, and so forth. In fact, check to see if this car is already in the Registry, and if not, shoot him an email, and give him the information below.
On the door post between the hinges, will be the serial # 51N-nnnnnn with N being 1 or 2 for Special or Deluxe, with nnnnn being the actual serial # of production. On the firewall, there is another plate starting 51NN-nnnn with the first N being 1 or 2 again, and the second N being the exact model ie 0, 1, 2 etc standing for various models, business coupe, Deluxe coupe, Traveler utility, 2dr sedan, 4 dr sedan. The nnnn with be the numbers of the body, as it was welded up awaiting assembly. These numbers do not exactly go lock step with the serial number, as different models would be produced at different times.
There would also be a bunch of numbers at various spots over and under various letter designations like TR, DR, AG, SCHED, ITEM, TRIM etc etc. Post those here and we can tell you how the car was produced at the factory, and where it was assembled.