I will chime in on the wheels piece as I went through this (and still am) on a 1960 C60 that I'm restoring.
Those look like Firestone RH-5 split rims. Look at the outer rear dual rim. There will be a Firestone logo stamped in with the script RH-5.
While most split rims are often referred to as "widow-makers", and while all split rims can fail during the inflation process if not assembled correctly, the Firestone RH-5 is by far the most dangerous and notorious one out there. If you spend some time searching the web and talking to folks that remember them, its really a matter of when they will fail vs. "if".
The reason the RH-5 is so notorious is that they are a 2 piece split rim vs. the "normal" 3 piece. There is no lock ring on an RH-5. The lip on each wheel half that holds them together are prone to rust pitting and metal-to-metal contact wear. You'll be forced to replace them if you buy tires as no tire shop will handle them. I never did find it in writing, but apparently they are even illegal to run down the road in some states.
If the tires are "low", do not put air in them, and certainly don't attempt to use one that has been run flat. The wheel halves can warp and if an RH-5 are sure to fail if re-inflated.
Other than looking for original one-piece wheels, I have only found them available at one source.
www.wheelsnowinc.com
The part number that should fit the 10 lug on 8 3/4 is 28160. Accuride used to make them, but now they are available from Wheels Now. They aren't cheap by any stretch of the imagination, but at least they're available. The wheels are only 6 3/4 wide so the biggest tire you'll probably be able to run is a 10R22.5.
I have taken a recent hiatus from my wheel search as the truck has been in for paint/cosmetic work since the fall, but chances are I'll end up having to get the new ones from wheels now. You may have better luck, but I spend a few months calling/looking around and wasn't able to come up with a set of 6 for my truck.
Great looking truck and good luck with the project. Its good to see somebody save the old iron.
Jonathon