Difference between optisparks in earlier and later lt1's
 

is there a difference between later aND earlier moder lt1' optisparks i know one has the vent tube but is there anything else. The GM rplacement is less expensive for a optispark for a later model Lt1

I'm pretty sure its just vented vs. nonvented

The later optisparks use a dowel pin cam drive while the earliers use a splined shaft drive, they're not compatible without swapping the cam, timing gear and timing cover.

Splined shaft drives are no good.... Fail more frequently the the dowl pin driven ones