I was thinking the same thing. If I wanted to go bigger than a T3/T04, than an external wastegate would be needed.
I see two ways, weld two runners together at the bottom, directly under the inside runners. Or have a shorty pipe go in between the manifold's turbo flange and the turbo's exhaust housing.
The manifold does not place the turbo in the spot I would have liked. It does not bring it completely up, rather of to the side. Because of this, I would build the shorty pipe equipped with an external gate to bring the turbo up some more, not to the side of the motor. If you have read Corky Bell's, Maximum Boost, you may know what I am talking about. Kill two birds with one stone.
The main thing is that there are welded supports for everything, which is what everybody has been complaining about with aftermarket manifolds.
Hope this helps.