Nice truck! The shop manuals sold by the Truck Shop, Jim Carter, etc. have detailed information and photos on transmission rebuilding. If your driveline is the same as a pick up truck, I think your 3 speed trans would be the same as is shown in the 1955 and later shop manuals.
I have found it is best to look for transmission repair shops that have been in business for a long time when trying to find one to work on my 3 speeds. Bigger cities usually have several old transmission repair shops.
