The fouler trick to restrict flow to the down stream O2 sensors works some times ,some times it don't . If you drill the foulers so the O2 fits ,you may destroy the fouler and then need to weld 2 foulers together to make it work . FYI the feds take a dim view of tampering the emission system on a vehicle if you get caught . The chances of getting caught are mighty slim . Non the less , in the long run you are better off replaceing the cats if they are bad. I have no horse in this race , and a'm just trying to steer you in the right direction .
