With the exception of color choices, decals, the luggage mounts/grab handle, and the windscreen mount they're the same. All of them will fit on either bike with no modifications.
The seats are very different in form and functionality, but they're still interchangeable. I keep the Strada seat on my Motard 95% of the time - it's more comfortable and less prone to shoving me into the tank. The Strada, Motard, and Motard SP all have different bar risers as well, and in the case of the SP the bar clamps and bars are different.
The only thing that isn't interchangeable is the power outlets; their mounting brackets are welded on to the Strada's frame and are not present on the Motard.