I built a school bus on a dually about the same year as your motorhome. The differential in a motorhome is usually 18 inches narrower, but with the same spring perch--pretty cool for me.
The front track is definitely wider than our AD's. I bought a 1 1/2 ton front clip for $60, they are usually pretty cheap. They are a little wider, longer and taller, but they bolt to the cowl and I made the half ton grill work.
You can check my burb/envoy build. I cut the fenders down and shortened the length for my half-ton burb. I think it is a better look than widening the inside edges of the fenders. You can look at the Hot Rod GM build--they did it that way and it appears they still have clearance issues.
