Yes you can run without a cat. The only thing you need is an o2 simulator of some sort. Theres the electrical ones which you need to splice/solder wires and are known to sometimes not work. And there are the "mechanical" ones, it is simply a spacer on the o2 bung so that the o2 sensor isn't as far in to the exhaust and it doesn't get a complete reading, in turn the ECU doesn't sense that the car is cat-less. Theres a thread about it somewhere on NAM...

 

I think this is how they work: o2 sensors detect temperature and turn it into an electrical current, or modify an electrical current based on temperature. With a cat, the temperature/current should be different before and after the cat, and the ECU expects this differential. If you run without a cat and don't want SES lights you need to "fool" the ECU with a false differential. This can be provided by the simulator chip, or by moving the sensor far enough out of the exhaust stream to produce sufficient temperature differential.
or not...

 

Msfitoy,

The first link below has some really good pictures and lots of comments about it. Enjoy.

http://www.ssrfanatic.com/forum/showthread.php?t=7208
http://www.hardcars.com/headerman/dodge/exhaust.jpg

 

Thanks bomboasy