I have cut out the cat on my truck and just welded in a O2 sensor bung on a chunk of 3in exhaust . I then made a spacer about 1/2in long, installed some stainless wool and threaded the O2 sensor in. No code sensor code and the truck runs quite well. I ran 3in straight pipe for awhile but it was quite noisy. I bought a cheap ebay super 40 knock-off muffler. I have less than $100 in my exhaust

 

You'll get plenty of pressure from your new exhaust from the cops