so apparently the cats on my car are all blocked up and fallling apart inside and pieces of the honeycomb have gotten lodged in the piping creating massive amounts of back pressure (over 15psi at 2k rpm). so i have some options. 1. buy a whole new exhaust manifold with the up and downstream cats from lexus - $1300 2. buy headers and have the furthest back cat replaced - ~$400-500 3. have the cats hollowed out and put back on if i can find someone to do it - ~$150-200. help me out here, what would be the easiest? and would the o2 sensors throw any codes if the cats are hollowed out or if headers were put on the car?