I have run offy aluminum spacers (1/2") on top of
the cast iron 66 intake to adapt Holleys. Most
feel that a "riser" will even out the flow after
the throttle blade and will keep the fuel-air
mixture from hitting the floor at high velocities
but historically Pontiac tri-power intakes do not suffer from that problem as they were well designed by the factory for their carbs.
Tom V.
