Scarry. Pinion brakes are not safe on the highway, not with a rig that big anyway. Unless his rear steer can be pinned for road use, I say that's a bad idea also. The front lift blocks are stacked and look suspiciously like 2x4s. You know that isn't 4wd right? The jacked up buses look like a fun toy, but I would discourage you if you are wanting to actually use the thing on the road. This is coming from someone who built a 2 1/2 ton rockwelled suburban on 1600x20's, the tire on that bus. I considered building a bus like that for a toy, but I wouldn't want to drive it to where I wheel, and trailering it presents a whole list of pains in the ass. Not to mention, it wouldn't fit down many trails and they really aren't capable off road, and what is it going to take to pull you out when you get stuck?
There are positives, getting the tires to fit is a sinch, the vehicle is strong enough to handle the tire size. The next tire size down, 1400x20 would fit on my bus with just fender trimming. If 4x4, you could make the brakes from the 6x6 work. The steering on the bus could handle the larger tires and probably wouldn't take much modification.
You might consider a bus that still has the older 20 inch rims and sawzall a set of 1400x20's on it. If you don't know already, that tire, and the ones in the link are military surplus. They can often be bought cheap as surplus from farm related tire stores. Don't skimp on them if you want to drive it on the road, find ones that look like new, they're out there.