Hopefully some O2 simulators might work. I had no cats in my altima, and the simulators worked great

 

1. Did ya read the description for "porting"? You cannot reshape the port when it's covered by that stupid cast-in exhaust manifold!
2. You'll "realize" more gains with just installing a header (if possible) compared to polishing the ports with that stupid cast-in manifold still there.
3. It needs to be sliced off, then fabricate a header plate.

No rocket science here folks, this mundane process of headers, porting, polishing, has been around for decades, and has not changed much.