Jim - A little digging through the web and the
GM Heritage Vehicle Information Kits provided what I think are the best pointers to help ID your transmission. This
on-topic post found in the old VCCA forum provides descriptions and pictures of where you can find the transmission casting number, casting date codes, and serial number locations on your truck top mounted shifter 3 speed. The info is the same for 1938-47 truck 3 speeds.
Also, the below pictures and extracts from the GM Heritage PDFs for 1946 and 1947 trucks confirm where you can find the stamped 3 speed serial number and info on how to decode where it was built. Once you find your information on the transmission, perhaps you can post pictures so we can help confirm what it is?
