I believe 39 and 40 fenders are the same as 41-46 fenders except they are wider. This is because the box on a 39-40 is narrower. I've seen Art Deco trucks with the earlier fenders on them to give an extra 2" of clearence for wider tires. The only problem is that the running board will not line up with the edge of the fender like it is supposed to if you go that route.
