Thanks, Ed for very informative research/ trial. I will also pursue what you have done.
I was talking to a dude in FVD. He said that I will get a CEL using 100cel CAT. He was saying that ECU needs to be reprogrammed to have engine recognize as if it has normal/ properly functioned CAT(400cel). Another words, 100cel is not enough to emulate normally functioned CAT. He didn't say that 100cel would not pass emission test. I don't think he can say that knowing that 100cel CAT would require mod on ECU.
Anyway, I think you are right. Header that I got from Che has a bung on the end of header. So I will install the front sensor like you recommended and I will plan to install O2 sensor with O2 sensor eliminator at the rear of 100cel CAT. By the way what kind of wires did you use to extend the wire to the back side of the engne? Do you know where to find temperature rated wire? Or you know where I can find extension wire for Bosch O2 sensor? Please advise. Thanks.

PS. Good luck on your experiment. I hope that works.