Well my memory isn't as good as it used to be but I would swear I saw pics of one being built now there is a possibility I have the pics in my mind confused with Dave's manifold.
Anyway, yes the tube on top was one 3" pipe with no baffles in it.
I have a pic in my head of the bottom end of the manifold as well but it's un clear

I believe it was just a spacer as in the 3" tube was welded on top of the spacer which was welded to the bottom half of the OE manifold, one big empty space in there. But I have no proof of this other than my scatted memories.
I am having one built here shortly and will be using the open plenum approach.