Something else related to porting that I forgot to mention-
The VFAQ doesn't mention this, and a lot of the porting guides I read didn't provide a clear explanation or didn't mention this. When you're porting your turbine housing, you can port the turbine outlet->o2 housing inlet to match your o2 housing as long as you leave enough to seal between that and the wastegate passage. Mark the size of the inlet of the o2 around the turbine outlet and start grinding, taking it in with a with a conical shape- porting less and less until you get within 1/2" an inch or so of the machined area by the turbine itself. You don't want to touch that. I think the VFAQ actually specifically said not to mess with the turbine outlet, then went on to say he had done something with it on another housing- the VFAQ is pretty confusing and not very detailed. The best indicator that I had done something right in porting the turbine outlet the way I did is that the Evo III turbine housing comes from the factory with this kind of outlet- if you can look at one of those, you'll see how to do it.

I matched mine to within an 1/8th inch of the opening of my Evo o2 which was as far as I could go while leaving a comfortable amount of sealing surface between the turbine and wastegate outlets. I only barely touched the opening of the Evo o2- I mostly ground down the indented bosses for the bolt holes, ground the boss for the o2 sensor down flush, ground out the step in the outlet and changed the angle of the wastegate path's entry into the exhaust by grinding the outside wall of the o2 in that area.