Tobin- You could shorten your frame, it's not all that hard. In fact, if you go to the Gallery here and look at Jim Schmidt's '40 3/4-ton, he's doing the exact same thing. I just sent him a nice 1/2-ton box to put on his ex-3/4-ton. I'm less than 4 hours away from you and can sell you a '40 1/2-ton frame or even a whole complete parts truck if you decide to go that way. I also have some steel fenders, but we can't sell parts here in the regular forums, so you will have to go to the swap meet and check out my ads there or email me. The front fenders are the same for 1/2 and 3/4-tonners. Big trucks (1-1/2 tons) use different fenders with a larger wheel opening for the larger tires. Can tell the difference by the notch in the front of the fender for the bumper bracket. The notch on a PU fender is taller than it is wide, the big fenders have a wide, shallow notch.
Also, since you are from Madison, find Eric Amlie from this board. He lives in Madison and has '37 and '59 pickups and knows a ton about old Chev. trucks. Eric can point you in the right direction. And he's a nice guy to boot!