Some connectors work. Spring cups work. Striker springs work. Certain triggers work, some need slight modification on trigger bar clearance area.
Sights, mags and barrel are not compatible.
Midwest finally started stocking threaded barrels for the full size pistol only, not the C, not the F, just the plain STR9. Reasonably priced at 80 bucks.
The magazines are not cheap but they are very well made. 35 ea is about as cheap as I've ever seen. The full size mag will fit in the C pistol. It will probably fit in the SC pistol also.
HINT, if you want to use a Clipdraw, on the full size or C, obtain the model made for the full size or compact Smith M&P, and carefully file about .017 from the back of the backplate. Carried one for years this way. Fitted it very snug so it required some gentle tapping with a plastic face hammer to seat it.