I'm certain that the V6's still Y-pipe, so from your exhaust manifolds on each side, they will come together at a Y pipe, and then single pipe to a single muffler on the driver side.
If that is the case, you'll need a midpipe (H or X pipe), and a muffler shop to weld those stock exhaust manifolds to the h/x pipe, and maybe put in a little custom tubing if it's not a direct fit. you'll also likely be looking at a catback for a GT, which has all the dual exhaust piping from the midpipe back, since you currently only have one pipe. You also need a GT bumper, or cut out from your v6 bumper for the exhaust tips, GT bumper is highly preferred if you care about the looks.