bypass cat and muffler???

Unless you are required to smog the vehicle by the DMV. I would eliminate the cat and muffler, run a single 2.5 inch all the way to the rear bumper. If your car is in good tune with good ignition it will probably produce minimal emissions. Mufflers are pointless on a full exhaust with a motor below 300 hp. I run no muffler on two cars, one is a 5.4 260 hp. It is mellow and nice out the bumper.