Side feed is about the only advantage. I don't think the plenum is any bigger and the runners are identical i think. (side feed is beneficial since all runners are supposed to get the same airflow whereas the centre feed the middle two runners get more air than the outside two because of the extra turns and distance involved) The other way to get around it is to cut the plenum off your stock manifold, weld a nice large uniform plenum on and use two stock throttle bodies situated between each runner for nice even flow.