Well if your going to do from the mnflds back you must be talking about getting the RAT DP,then yes your o2 sensor will fit and the piece with the cat is legal ,go with the 3" dp ,for the cat back you have many choices and they are all good ,stainless is the best,next is aluminized steel then plain uncoated steel (which is what most exhaust shops use) you ca'nt get 100% aluminum pipeing for exhaust,the stainless will last the life of the car but is more expensive ,a good choice would be the GM stainless cat back around $500 I think.