Re: bypassing the catalytic converter
The point of going without a cat is to reduce back pressure. It sounds like a good idea, but the air flow going from the headers to about after the flex pipe is the most important in reducing backpressure. the turns the exhaust has to take to bypass the cat would cause back pressure. the y pipe that you would fit in there would also caust back pressure no matter which path you have open because its not smooth.
Personally, I would weld in an lx downpipe with no cat, and then make the cat on the bypass pipe. a lot of work, but you could have an electronic switch when you get to a certain rpm so you could have good tq at low end and hp at high end. plus youd fool the emissions people XD
Totaled my Civic LX, bought an RSX Type-S