Like BCB00GT said, if you can reuse the stock gaskets, go for it. Whatever you do, don't buy them from ford, they are an incredible rip off. Summit sells them for like $20 for the set. I also took some Red RTV sealant and put a thin bead of it around there, the last thing you want after all that work is to find out there's an exaust leak and have to tear it apart and do it all over again.
Good luck with the install, and yes, the O2 extensions (or equivalent) are a must.