Finding the dually is going to be your problem. W350's are hard to find and bring top dollar.
Now on these old Dodges if your going to do a paint job. Remove all the old paint. The original primer most likely has rust under. I ran into this problem on my truck and many other 1st gen owners have seen it also. My cab came out of WY. The paint looked good no rust showing, very few scratch in the original paint. It was the wrong color I wanted. So I started sanding. What I found was small rust spots under the primer. There was a speck in about every square inch of the panels. Some specks needed spot putty after primer was applied. These were under paint that would have buffed out to a factory shine if it had been the correct color.