The SBC damper has to be installed fully so it "sandwiches" the crank gear between the crank and the damper snout. The Vortec damper from a reluctor wheel-equipped engine is shorter by the thickness of the reluctor. So if a reluctor-equipped Vortec damper is used, a spacer made from the reluctor needs to be used if a steel timing cover is going to be used.
This is because the reluctor ring won't fit behind the steel cover. Without the spacer, the damper will go on too far and the pulleys won't line up, and the damper might even bottom out on the timing cover.