It SOUNDS like you have Daytons. If you currently have 10.00-20 tube tires a set of 11R22.5 tubeless rims should bolt right on no problem and will give you the same overall diameter as you have now. I was quoted about $100 per rim new and tires run the gamut.
If your current tires are small, say 9.00-20 you will have to be a little more careful about spacing and clearances, but you shouldn't have any problems. Any reputable commercial tire shop should be able to help you figure it out.
sorry guys got ahead of my self this morning trying yo get out the door to find an answer. The buss has 8.25x20 budd style 6 lug rims. I would consider changing the front rotors out if I have to for some 10 lug ones if they make them. My wheels now have the ring that comes off.
The axle and hubs aren't likely going to be the issue. Chances are you're going to have the same mounting pattern on a new axle unless you have smaller rims right now. Even then...Steve managed to get something going on his bus with the smaller rims. When you start talking about axle and hub swaps you're talking about brake swaps too which must be matched to the rest of the system, steering, blah blah blah.....I would just talk to your local commercial tire place and see what they tell you.
thanks guys I have found out that gm made a 10 lug hub and rotor that will fit my spindle on the front axle. Now just got to find them or a whole axle. I will give the folks a call about the wheels. Way cheaper than the ones I priced here.