There seems to be a fair bit of overthinkage here. Some of the ideas are good, but damn expensive.
I've got a E-450 short bus with the same weight ratings. The 225/75 tires these things typically use have a far lower rating than your average Load Range E truck tire. One thing you can do (which I've done) is to mount 265/75-16 Load Range E tires on the fronts and rear outers, and 235/85-16 on the rear inners and spare rim. Tire diameter is the same. and the narrower inner tires keep the pair from scrubbing against eachother and building heat. To use 265's on the inners would require 2" spacers between the dual wheels...which will increase your track width and make it even harder to stuff down that skinny little trail to the river bank. And yeah, they recommend a 7" rim for 265's and all that...but people install 265's on 6" dually rims all the time and it works just fine. Myself included. I got Kenda Klever M/T's. Cheap, steel belted 3-ply sidewalls. Damn tough tires with good grip. Fookin' loud on the highway...but its a camper and not your daily driver.
Re: Spacers - 2" spacers are the narrowest you can use without cutting the wheel studs down...which would then necessitate the use of spacers in the future.
Here's a photo of my DIY suspension lift. I made the 2.25" rear block from a 1.5" chunk of 3x6 steel tube, .375 plate and a bolt. Bought new U-bolts longer than stock. On the front, I bought the spring spacers off Ebay for 2wd F350, and had to flip the big Jesus bolt upside down to make them work. Alignment guy fixed the camber, but caster is right at the limit of acceptability. Fabbing a radius arm drop would fix this, but this truck will probably get Weldtec suspension next spring.
