Grinderman,
At least according to the parts lists that we have, there were no changes to the horizontal countershaft assembly from beginning to end. The only other countershaft that you could buy up until sometime in 1945 was the Vertical Countershaft. The 10-107X Spindle Assembly is used on both.
I believe that you mentioned earlier that as received, your countershaft assembly had a felt or similar material washer between the left-hand bearing and the 2-step pulley and the pulley had a groove on the right end of the hub that the felt washer fit into. If I am not mistaken, that may be a modification made by a previous owner. According to all of the various vintage parts lists that we have (dated from 1942 through 1966), the 10-107X originally came with four 9-111 fiber washers, one on each side of each of the two straight roller bearings. And no groove in the right face of the original 9-427 2-step pulley. I suspect that the PO was just using too much grease.