The 1940 washer kits will not hurt, though in a couple of places the washers might be too big. Our experience is that the oversized fender washers are too soft, and when tightened down distort enough so there is actually more force exerted on the fender than with a more standard washer.
What we recommend is to use hardened 5/18 USS washers. They will spread the bolt force across the whole washer area, not just next to the bolt. Also, open the holes in the fender to about 1/2" so the fender has wiggle room for adjustment and to avoid lateral stress on the side of a bolt hole.