You can install a vented optispark 3 ways. Only 1 is correct. The dowel pin has to go into the correct slot which looks a little different than the other 2.
This is the back of a vented Opti
Here is a comparison pic between the 2
Here is the correct place on the back of the vented opti which the dowel pin must go. His finger is pointing to the correct slot, it looks slightly different from the others:
You MUST loctite the screws onto the rotor, and tighten them hard. If you fail to do this, they will back out, then the rotor will wobble, shatter, or shear the bolt heads off. This happens a lot when people replace the cap and rotor.