On my coil pack for a '94 Clubman there are 3 holes for bolts on the bracket to attach it to the back of the engine. Mine's only held on by 2 bolts on the left and right of the bracket, the third bolt in the bottom centre of the bracket was not there when i took of my coil pack. The 2 bolts seem to hold the bracket firmly in place though. I just measured the 2 bolts that i have securing it and they have a 12mm head and are approx 20mm in length.
You can see my old coil pack which i burnt out in this thread:
viewtopic.php?f=29&t=42339Hope that helps.
AK