I got a this code p0420 I know it's for the cat but my car has obx headers and 2.5 inch exhaust with mag hfc so I hear in have to get the spark plug non foulers or the o2 spacers to trick the ecu I just don't know which one to get this blox one or the dorman one I got a pic below

 

The forum can sometimes be slow in responding, i dont know the answer but if you have facebook, join the group and its a lot quicker.
facebook.com/groups/183877908331009

 

Either one is ok