Inliners International Forums General Discussion Engines General intake manifold design question?

I have manifolds for my 153, which I've been driving. The issue is the 3.0 Mercruiser which has 8 individual intake and exhaust ports which are much larger, and shaped differently than the 5 ports on the 153, three of which combine two cylinders. I'm just trying to sort out some of the basic parameters. Like can the two barrel carb be parallel to the head like it is on the marine "log" combo manifold without losing performance or efficiency, and is a "carb box" really necessary as a larger chamber before the leaders into the head?