Good stuff man. Apparently the front subframe bushing holes in an M3 are ever so slightly larger (2 mm, or 0.080") than on the 325s, I suspect it’s the same for the 318s. It’s no biggie though. I think the vendors tend to specify the M3 bushings for the non-Ms anyways seeing as it’s a better fit.
What will you be doing for trailing arms? As I’m sure you know, the M3 stuff is noticeably different (and stronger) here with larger axle and bearing diameters.