1947 was a transition year. The early series used a sliding gear that had been used since about 1940 and the late series may have used a SM420 that was used for about 20 years. Most of the 1947 models used the old sliding gear transmission. Books cite the SM420 as being offered in late 1947, but all I have ever seen is the sliding gear type. There is a difference in the bolt pattern in the two transmissions.