Your existing bell housing for your '46 should be Casting# 839257 per the 1929-54 Chevy Master Parts Book (excerpt below). It's listed as used on all 1938-47 Commercial and Utility Trucks, with no specific transmission listed. Same part listed in later 1957 and 1962 versions of the Chevy Master Parts Books. So confirmed it will support both the 3 and 4 speed transmissions.
Not sure where you got the "839210" number as it doesn't show in any of my Chevrolet Master Parts Books for truck bell housings.
Sounds like it's time to move on to the next step.
