They make several different adapters, the fully open type will be the least restrictive.
Even with that said if it's going on a dual plane intake with a divider in it you may need to put a divider in the spacer/adapter as well.
I've done a lot of testing with spacers and such and have ran into a few scenarios where using an open spacer or adapter on a dual plane intake that has a full divider in it caused running issues.......Cliff