From the owner :
"Just bore it out to match the 38mm hole diameter. The standard mig welder isn't going to work if you want to make it like mine. I believe my welder used some kind of tig technique with mine where he used a single stick of cast rod to weld with. I'm not sure exactly how my guy does it, but he is good. When he got done with it the manifold looked sick. It looked like it had came stock that way. Over time the manifold where the metal was smoothed over on top has became slighlty porus and leaks very slightly. Not enough to hear a leak, but enough to see where it leaks a tiny bit on the edge of the wastegate. When i had it brazed on though it leaked like a son of a bitch after about a year. The flange actually fell off completely while i was on the way to the welder's shop lol. Dont expect a braze to hold up on it."
his username on honda-tech is, "SOHC_MShue"