I currently am throwing a P0420 code, I live in California, I replaced the afr upstream and the oxygen sensor downstream. Engine was recently rebuilt, I did a valve adjustment, new gaskets everywhere same with sensors. I've done some looking around and can't find an aftermarket or oem dealer replacement. Idk what to do, I need to smog it, all monitors set except the catalyst, when it does set it throws the p0420 code. I'm at my wits end, can anyone shed some light and help me out??