No rear O2 sensor

Hey Fellow Jeepers, I have a 1996 XJ Country and the exhaust system passed air care with flying colors but the pipe below header flange has a huge dent in it and the muffler is so rusty I can probably poke my finger through it. The cat looks ok.
The reason for this post is I bought a second hand exhaust system from a 93 XJ that had a stroker engine The exhaust system is 2.5 & only 2 years old and has a High flow cat and high flow K2 muffler but the cat has no O2 sensor and my 1996 has the rear O2 sensor in the rear of the stock cat...
Should I just cut off the high flow cat and put on my stock cat and count my blessings or is there a way that won`t throw everything out of wack ?
I have read about the O2 sim cel fix http://www.bigdaddiesgarage.com/?gclid=CJOMh9-bn6UCFQUSbAodgFXBIA And the black box but it won`t give accurate enough reads as posted here http://reviews.ebay.com/Truth-about-O2-simulators_W0QQugidZ10000000002812356
Alot of info crammed in that article and it will take me a few more reads before I can comprehend it so anyone with this type of expertise or experience your time is appreciated and thanks in advance for your reply:wantyou:

1-the dent is stock and should be there-normal--
2-High flow cats are not needed,cut it out ,put the 96 cat in,replace the muffler and call it a day.

I'm with Wayne Sihler on this.

The after-CAT sensor does not effect emmisions of the engine, it is strictly a nanny-sensor to tell the PCM if the CAT is doing its job (kind of like a little sister that rats you out to dad). Its absence will throw a code.

You could add a bung to the exhaust after the high-flow CAT or just use your old CAT.