Upgrading the stock dual exhaust won't provide much performance gains on a mostly stock car other than noise. If you do want a little more grumble, some DynoMax ultraflos should do nicely
If you want that behemoth to respond a little quicker, try a xcal2 performance tune from
www.blueovalchips.com, and a 03-04 Mercury Marauder airbox at the same time
To use the MM box in your TC, you will need to use hole-saw on bottom lid to hook up to stock intake tract. On your -02, you will also need to drill a hole in the airbox lid for the IAT sensor. The stock connector plugs right into the MM airbox's 10mm larger 80mm MAF. The airbox itself drops right inplace of the stock unit.
Besides an increase in power, the tune will also make the transmission shift schedules and converter lockup sportier and more refined feeling. It will really change the way the car drives.
Swapping out the rear gears to 3.55 or 3.73 will help the car accelerate a little quicker. I'd go with 3.55 only because with a 3.73+ ratio and that long driveshaft you may experience driveline harmonics at higher speeds if you travel highway a lot. If you really only drive around town, 3.73!