wow this is an old thread bump.
it has always been said convertible seats won't swap for a few reasons. this is the first of hearing the bolt holes don't fit. Not sure if that's because the convertibles have different metal welded in to make the seat attachments stronger. but I know M3 coupe seats fit a 323Ci, so it's not a 323 thing.
OE CSL WHEELS - OE CSL BRAKES - OE AUTOFLD MIRRORS - CSL RACK - CSL TRUNK - CSL DIFFUSER - AA TUNE - AA PULLEYS - AS 40% SSK - BILSTEIN PSS9s
CF CSL LIP - NAV- BMWP CF STRUT BAR - BMW GROUP N MNTS - GRUPPE M CF INTAKE - SUPERSPRINT - UUC S/S LINES, RTABs - H&R SWAYS - 4.10 M-SPORT DIFF