Yes I think they do right out of the box. Much less how he mods them. You need to keep something in mind. The outlet size is NOT the end all be all. It's is only one part of the picture. The rest of the manifold......how it's shaped, the runner size......all of that plays an integral part.
Some of the Ford 351C 4V manifolds were some of the best flowing manifolds ever, yet they had only a 2" outlet. It's all about velocity.