Steve I started in the direction you are talking even got as far as mounting the box (a mid 80s 4X4 box)
http://rides.webshots.com/photo/2418906350096773078KeHMYq the problem I ran into may or may not affect your build, with the 10.00X22.5s on my truck I ran into clearance problems in a right hand turn the tire would hit the box, draglink, and pitman arm. I know this setup woks great for the smaller trucks in fact it was from a tech article in Classic Truck if you have a Saginaw box that bolts to the outside frame rail try bolting it as far forward as you can and with the front tires off the ground check for clearance if you have the room to turn right you have it made if not you may think about a scout box like Grigg and I have used.
If you wish you can have the box that didn’t work for me and I will see if I can find the tech article for ya.
