the answer is vague. Typically open spacers increase higher RPM hp since they increase the volume of the plenum. Four-hole spacers sometimes increase torque since they keep the velocity and sorta kinda increase the runner length. The confusion comes because some spacers hurt power when they should help, and some hurt torque when they should help. If I've learned anything from car craft and hot rod, its that you can't predict how a spacer will affect power other than past experience.
In general, I would suggest a four-hole spacer, but check first... chances are you don't need an adapter. Most spreadbore intakes are drilled with both carb bolt patterns. Pull the carb and see if the intake has 8 bolt holes. Putting a square on a spread intake is fine if that's the case. The problem comes when putting a spread carb on a square intake. The secondaries have to make such a radical transition to the plenum that it never works right, but no worries going from square carb to spread intake.