O2 sensor location?/ exhaust upgrades

I just purchased my second XJ, a 2001 sport. I was looking into exhaust mods but I dont want to set off engine lights with the o2 sensors. I have located 2 o2 sensors on the manifold but I can not find an 02 sensor behind the cat. Everywhere I check says that there is a downstream o2 sensor, but I cant find one to the rear of or in the cat. does anyone know where this sensor is. Secondly, if I install a banks torquetube header97-01 XJ, does it have provisions for the 2 o2 sensors that the manifold has and will it affect the computer to install it?

Are there four O2 sensors in the manifold, (1 )on each side of the two precats?

should be 2 on the manifold and 1 behind the cat. but im not positive

My 01 has four O2 sensors. The exhaust manifold has two mini-cats and a third cat, just in front of the muffler. Two of the O2 sensors are located above the mini-cats and two more below the mini-cats.
They are sort of hard to see from the top. View from the bottom, using a flashlight.

Both of the O2 sensors died on my 97 Dakota at 75,000 miles.
The XJ has 72,000 miles, so I'm expecting them to go soon .
It's going to take a bank loan to pay for four of them when the day comes.