You want a turbo back, see "flying skyline gtst dump and front pipe in 1 nr" on ebay.au . Cost me a total of $300 with all the shipping and bank wiring fees. I have a pic of it on
http://www.imagestation.com/members/jabello comparing it with the stock O2 housing. It does come with a bung for the O2 sensor. I think it took a week to arrive from Australia to Cali.
I would have just gone with Macks but they did not have it yet. I wouldn't buy the other (competition) company's down pipe however since I saw the quality of test pipe that they sell.