The M104 straight 6 ( and the 4 cylinder version as well ) have two types of ignition coils but I've been unable to come up with any specs. I suspect it has something to do with primary resistance but have no proof.
The split interweaves a bit but it looks to be 96 and older ( HFM_SFI injection / ignition control ) has UF137 ( standard motor part brand ) 0 001 500 280, 0 001 587 003, ( Bosch ? ) 88921409, E537A


and 97 up ( ME SFI 2.1 injection / ignition control ) UF527 ( standard motor part brand ) 0 001 587 503 ( Bosch ? )

Any ideas? Thanks