My 3800 DRW sits on the same axle as a single rear wheel. The front wheels have a spacer that bolts to the front hub to push the wheel out and allow for the use of the same dual type wheels as in the back and maintain track.
Basically besides the possible difference in springs that John mentioned, Single Rear to Dual Rear would need 6 dual type wheels and the front hub spacers. Dual rear to Single rear would be the elimination of the front hub spacers and 4 appropriate wheels.
