4.3in84toy:
According to the parts books, the carrier was the same for all '39-'46 (mech. shift) 2-spd. rears. According to the specs, those years all had the same ratios, too. I think that's through '46 first design.
From what I can tell, all 2-spd chunks from '39-'55.1 would bolt to any '39-'55.1 2-spd housing. As far as direct interchange goes, I can't say for sure, since axles (splines) and internal components changed over the years.
