My understanding is that the cabs are about 2 inches shorter on the 39 and 40 than they are on the 41-46. I believe this causes the wheelbase to also grow on the 41-46 as compared to the 39 and 40. I have a 1940 3/4 ton longbed. I don't believe the longbeds are that out of proportion on the 1940. I might have prefered a shortbed, but I will not part with my longbed.