I don't have the list in front of me, but fewer than you'd think.
The magazines and RSAs are the same within caliber. The SD sights are M&P compatible, but not SW. The sear assemblies are the main parts changed from SW to SD and don't interchange. Several small parts, like trigger return springs, are the same in SW, SD, and M&Ps.
Some add-ons are in the "can be made to work" category.
APEX kits for SD are unique to SD.
