I reamed mine out. Andy at ssc attached the reamer to a drill and it was done in no time. Never heard anyone using BMW fittings before.
Click to see my build photos on Flikr
Saturn MX5 Based Chassis, Limited Slip Diff & 2.4 Quick Rack.
Build cost.... seems to be spending more on tools than car bits at the moment! (they will be handy in the future though).
Car iva'd and passed 15/08/2014. Finished weight 572kg.