Find a junked 5/6 series of similar vintage. I converted an '87 635csi with a friend's professional help. You'll need the transmission, driveshaft, pedal assembly, new hydraulics & clutch parts. The conversion is worth it, if you love this car. Buy a sport shifter & install while the transmission is out of the car. I lucked out with finding a 5 speed in great condition. The donor car was junked due to an obvious engine mishap. The oil sump was blown out from road debris. I spent more on the metric mechanic shifter than I did on the donor car.