Building An O2 Housing

[Blurred Talon]

I've got a Chinese O2 housing on my car currently, I've got the dump tube cut off and was going to have my neighbor TIG weld a sch 40 pipe on for my Tial MVS. However he brought to my attention how shitty the tube outlet is. It's maybe a 1.5 and a serious restriction. I thought about buying a new housing made for a Tial MVS gate but my neighbor suggested we could just hack off what's there and weld some nice 2.5" SS to it (turbo is a Evo 3 16G).
How hard would it be to do this? My main concern is having it fit up on the car (I think the housing is the source of my current exhaust mounting issues or my Megan Racing DP).

 

[1997_GSX]

Is it 1.5" on the wg port or the exhaust discharge port? 1.5" for an MVS is the right size if it is on the wg side. 1.75" is the right size for a MVR 44mm.

 

[Blurred Talon]

Exhaust port.
The wastegate discharge has already been removed and will be replaced by a 1.5" sch 40 elbow if I go ahead with this.