http://youtu.be/I6rIJAO01XA

I have performed a video borescope of my 2008 Triumph Speedmaster TOR exhaust. A long time ago I read somewhere saying the removal of O2 sensors or SAI (don't remember which) could force clogging of the pre-cats. Well, I do not believe this can happen, but anyway it is obvious none are installed in my stock headers.
As you can see, after the muffler, when entering the header, the first hole is the duct that connects to the other header. Then a view of the plug I installed where the O2 sensor used to be, and finally the exhaust valves with the tiny hole for the SAI.

Note the change in colour in the valve in front of the SAI hole due temperature difference