So i'm about to order an O2 simulator, a hi-flow cat from magnaflow, and a ws2 exhaust. My main question is what is the diameter of the hiflow cat and if it is different than the ws2(which i think is like 2.3 inches) how do they join? would they come with all the things i need? If it has any effect, I have a dc 421 header as well.

 

does the cat bolt on or is it open-ended so it can be welded into your exhaust system? If its bolt on, it will PROBABLY bolt right up the header, but if not you can always weld a custom flange on tehre so that it bolts right up. As far as different diameters go, a muffler shop can custom bend a pipe to fit the diameter you need. Hopefuly the cat is bigger than the catback, that way it wont be restrictive.