I would try and find a carb spacer that divides the sides like the intake. It doesn't make much sense to me to run a dual plane intake if you basically make it a single plane by putting on an open spacer.
Here is a link to Edelbrock spacers, look at #8714 & #8715 they even call them "Performer".
http://www.edelbrock.com/automotive/install1.html
Chuck