here in NJ they "look" for your cat, and obd scan for codes. i got a 50 dollar hi flow cat welded in. you can have a shop do that. as well as move the o2 bung. sd headers have a mid pipe in the down pipe, remove that pipe install the cat in its place. easy. you could band clamp the cat in place if need be. i did to get through inspection.

you need a tune with the cat and rear o2 deleted and you'll pass no problem.