Exhaust questions from new guy

[dyna962007]

I have a question.I have a 2003 stock 350Z.The exhaust has both sides of the engine going into a single pipe system to the rear.I'd like to seperate this into two independent pipes with a crossover pipe. Not run both sides through one muffler.I cant tell from most of the systems I see for sale, if this can be done.I'd like to use as much of or some of the stock parts if possible and I like the way and where the exhaust pipes currently exit the back of the car.Also, I dont have the money to install headrs right now, but want to later.If I do the exhaust job now, can I install the headers later? Will they still bolt up and in the same location? I guess what I mean is do aftermarket headers usually fit up to and bolt right up to stock exhaust systems?THanks guys, Mike