what is the difference between the 93-94 and a 95-97 opti spark distributor?

 

==There are two slightly different versions of the Opti-Spark distributor manufactured by GM. The first design version was made between 1992 and 1994. Other than some small vent holes, the first design Opti-Spark had no provision for evacuating built-up moisture. Also, the caustic ozone gases created by the ignition process were also left inside the distributor with no vacuum removal. This design was replaced in 1995 with a vacuum-vented Opti-Spark (1994 B-Body cars received the updated Opti-Spark before the F-and Y-Body cars). Along with the new venting provision, the second design featured a redesigned cam drive and a different electrical connector.

This was in one of Pete's writeups.