Hello Brad,

I am not going to be any help but I noticed in the parts book that there are two different part numbers for 41-47 3 speed transmissions and 48-53 three speed transmissions under the "commerical" heading. In the notes for the "commercial" 3 speed transmission it says something about a 3/4 ton truck. Hard telling what the difference is in part numbers. Maybe something simple to swap but maybe a completely different design. Hopefully someone with some direct knowledge will chime in

http://chevy.oldcarmanualproject.com/parts/1929_54/251.htm