The Caprice we pulled the engine out of was an early '94 car, so we ordered the '94 1/2-and-earlier distributor from MSD. With O-ring seals, better venting, a beefy one-piece billet base, and a more sensitive optical pickup, it is the Optispark to have. Once we got our original out though, we noticed that the way it indexes to the cam is different. On the left is our old unit, which is a '94 1/2-and-up distributor (MSD replacement PN 83811). On the right is the '94
1/2-and-earlier model (MSD PN 8381). The car we pulled the engine out of got a crate engine in '02 (thanks LAPD), so the crate LT1 had the updated distributor even though our car should have had the early one. Do yourself a favor and pull yours to look before ordering.