I've recently worked on my 37 3-speed, and would agree with the suggestion to get the shop manual. I also found the master parts book to be helpful in determining what fits between what years.
I found replacement bearings on Ebay as well as replacement gears.
Also, a 37 car transmission uses the same basic gears, except that the truck has a longer output shaft (transmission is longer to fit in the same space as a 4-speed.)
