I had the post just before yours, and as I said, I just finished a restoration of a 47 H. I had the same situation but had about a quarter inch of vertical play. I had torn the entire tractor completely apart so it was easy to see where the problem was. At some time the tractor's bolster thrust bearing had gone out. According to an old timer friend which was a former IH mechanic, this happened often. This problem is not noticable until the tractor is jacked up. There is not supposed to be any play other than a small amount to keep the gear from wearing on the bolster casting. Mine had worn enough that I had to have the shaft built up at the bearing seat.
Hope this helps