Buy the y pipe,
you prob. cant get the stock y to work b/c it is 2.5 or so and the header collectors are bigger, I mean anything can be mated up with a welder and torch, but even with the New y pipe it is a pain to get lined up.
If you didnt get any instructions with your headers like mine they both go in better from the bottom, I had to trim a little off of the tranny bell housing to get good clearance. Reciprocating saw will fix it up, and leave all the header boltes loose until you get the y pipe in loose, makes it alot easier assuming you have the same long tube headers with offroad y pipe that I have.Hope this helps.