I have a S420 ,MAF failed,and the previous owner drove the car long enough like that,till one of the front cats is almost plugged,will start to lose power after 10-15 miles of driving and showing the o2 and cat code.If I don't need to go thru emission,is it possible to remove all four,or just the front cats and replace them with custom exhaust pipe?,I have a local,inexpensive muffler shop that works well on making custom exhaust that will fit any car.Aside from check engine light,any other issues to expect?