Call Rogue Engineering. They'll hook you up. They already did an E46 S54 conversion and are willing to do other conversions. Have been thinking about the E46 sedan S54 conversion. We'll see... thinking about kjust waiting for the E90 4dr M3 and S/C my car at some point after a few Drivers Ed courses and some racing wheel time.
And Nick, companies like Technik/Infinitas have been S/C cars without any problems after 5yrs.