[Kube]

Jim is correct in regard to the generator mounting area and vacuum port(s) being different. 1938... all were aluminum while 1939 had a mix of aluminum and cast iron intakes. 1940 - '41 were all cast iron. 1938 - 1941 appeared very much the same. Of course the aluminum intakes, while identical to themselves were different than the cast iron intakes of those same years. All had two vacuum ports near the block mounting surface.
The 1942 - 1948 intakes were very different from the earlier designs. All were cast iron. The shape of the carburetor mounting base was different than the earlier design as was the area where the generator mounted. Also, they now had but one vacuum port, that being "moved" to just below the carburetor mounting flange.