This is a good thread:
Bottom line, I wouldn't do it and not only because you have to replace parts. The M3 has a different braking system entirely (different master cylinder) ... who knows what kind of effect that will have on braking performance.
Quaife LSD, JRZ RS Pro, JRZ camber plates, Eibach ERS, full M3 susp, custom toe arms, Powergrid end-links, SS brake lines, brake ducting, Michelin PSS, UUC SSK, ETS FMIC, ER CP, Perf. Exhaust, VAC RSIK + Sparcos; work by VAC Motorsports in Philadelphia