Great question. The "621" bellhousing is the most common bell and one that we've used for years. There are probably others that will work, but I would suggest comparing with scrutiny to be sure they are the same. Things we'd look for are the bolt pattern on the transmission side, be sure there is enough "meat" to bolt the transmission up. Also the opening for the clutch fork should be at 9 o'clock as shown in the photos on our website. Small differences is usually when problems arise.
