Thanks for raising this point Rick. A call to Dalyn at Griffin answered the question. BMW uses 12mm, Ford and GM use 17mm pilot. I did have a problem with bellhousing length though. Kennedy and Quicktime bells are made for DeTomaso witch has a longer input. Griffins RBT is a bit short when used with Kennedy or Quicktime and raised concerns. I made my own pilot bushing and cut 1/8 " of each end of the bellhousing
I suggest to all to double check all dimensions. We had P1116 with a "BMW M1" ZF-2 and the input shaft is a couple MM longer than a GT40 type. Took all of 5 miles to wipe the thrust bearings out of the engine! Both the diameter and length are things to be aware of.