I can confirm this later if nobody else does but I'm pretty sure I heard the actual housing IS narrower. As in there's not enough room to actually move the perches. I'm hoping someone else can confirm so I don't have to crawl under my parts truck in the snow lol!
I’m not 100% sure, but I think a SWR and a C&C axle are about the same width, with the spring pads in a different location. The DWR axle is much wider, something like 6+ inches wider.
A C&C has a frame width of 36 inches and is fairly straight and flat. A truck that has a pickup box is wider, and had a “hump” in the middle.
A C&C dually uses a SWR width axle also, since the frame rails are narrower, the duals will fit.
So, I believe;
SWR Pickup, and C&C SWR or Dually use a similar width axle
DWR (dually) Pickup, much wider rear axle.
A 4x4 uses the same width front axle. The difference is at the wheel, with a dually hub, or dually adapters.