headers would be kind of tough to recreate, but you can get the y pipe on craigslist for pretty cheap.
I was just batting the idea around with updating the 300zx exhaust with the 350z exhaust. I don't know that I wanted to drop the coin to do a full exhaust set up, but the piping on our car is all rusted, and holey and beat up and since stock 350z exhaust is cheaper than some of the 300zx options, i thought that might be a fun way to go, especially if it gains some of that 350 exhaust tone.