two 2.25 band clamps, two, 3 inch band clamps, unless you need a cat, then you can weld the cat in and not need the two 3 inch clamps.

reuse the stock head to manifold gaskets. toss all the gaskets and clamps they give you in the trash, all but the cat back gasket, use that one.

yes you need a o2 extension. and maybe a new rear o2 if yours dont come out the dp. or a tune with the rear o2 deleted. you will need a tune for this.