I always think it is a good idea to put a long bolt in the distributor drive gear to prevent it from falling into the gearbox when the distributor is out. When you have removed the dizzy, look down the hole. (a torch helps) the thing at the end with the slot across it is the dizzy drive gear. it has a bolt thread in the middle of the end of it, can't remember the size.
Not so important if you are leaving the dizzy mounting plate in the block, but trust me, if you are taking that out too, it is worth it
Cheers
matt