here is another kit, but its 3" also. http://www.cl***icparts.com/1947-53-Rear-End-C-Notch-Kit/productinfo/93-314A/ or something like this should get you enough clearance http://www.kplinks.com/product.php?productid=162&cat=81&page=1 leonard
I did some measuring and bottom of frame to top of axle is 2 inches less than the running boards to the ground so a 3 inch notch should hopefully be enough
Depending on your tire size it may not be. For more drop than 3", you will need a step or bridge notch. A simple notch will not be enough. None specific for an AD truck that I know of. They don't need to be. Once you have gone that far, a universal one will do, or make your own.
Hate to poo-poo on any vendors but the CPP AD truck notch is total sh**. I ordered one and it didn't fit either 47-53 or 54-55 frames at all. I don't mean a bend here, bend there I mean flat out wrong. Called, e-mailed, sent pics, and never got a resolution until I posted it in another forum. I should have known when the advertised p/n, my order p/n and the p/n on the website were all different. wound up just making one which I should have done in the first place. Oh yeah, with 28" tires the 3" notch puts my running boards about 3" off the ground.
Ok, forget I mentioned it. Step notch from Gambino, then. You can talk directly to Alex if you need any help, too. He's a real stand-up guy.