The XH1042 isn't necessarily locked into a short lug impulse drive cup. Drive cups between C and X magnetos are interchangeable. The WICO C was first used on the Model "H" when it was launched in 1939, and was then used on all of the flange-mounted Waterloo tractors until the better-designed WICO X was available sometime around 1947 or 1948. The C and then the X became the appropriate "repair parts" as time went on. Deere told dealers that they didn't have to stock all the various unique assemblies of magnetos but could stock a few magnetos along with the appropriate impulse drive cups to swap as required to suit the application. The picture is from Field Service Bulletin 159-S, January 1948, soon after the X was introduced, and take a look in the table at note #3.