I recently bought a 95 GS-T and it already had a Pacesetter downpipe on it, which is connected to the stock cat and exhaust. I wanted to buy the GT downpipe from Apexi but i live in Chicago so I wont pass emissions

so I decided to stick with the Pacesetter downpipe but my question is this:
If I get the Apexi N1 exhaust, the piping on that system is 3" so how will it bolt or hook up to the stock cat? Will I have to get a 3" cat or does the Apexi N1 catback come with some kind of adapter to hook up to the stock cat? What are my options?