I can't remember if you have the 4.7 or the Hemi. If you have the HEMI, this is what I did:
I bought an entire exhaust from a 8K mile Cherokee SRT8 (6.1 HEMI). THese are true stainless headers with thick flanges, bigger collectors, bigger cats and both pipes come into 1 muffler.
I threw the cat-back away.
I will cut the 3 foot muffler out because it weighs a million pounds and doesn't flow worth a crap, and replace it with a 2 into 1 system (2.5" x 2 into 1 x 3" outlet) and run the 3" in front of the passenger rear tire.
I bet you can buy everything I bought right off an SRT8 forum for $300 - $500 because its been sitting in someones garage for 3 years now and their wife is steaming hot mad about it.
THe headers will be a b1tch to put on and therefore removing the head is sound advice.................BUT.................if you remove the head, consider milling the head .030 to up your compression to 10.5:1 (static)
BUT...............since you are going to all that trouble, I highly suggest you change out the cam (maybe a 212/212, 518/518 on 114 lsa) and an SRT8 crank pully (under drive).
Now you need a Diablo tuner and have someone (i know a few) tune it out for you. That combo will make right about 385 / 385 at the wheels and at that point you really need a locker because you'll spin them regularly without fail and consider the suspension, you'll wheel hop till you break something.
And yes, that will out run most stock Mustangs, Cameros and most all ricers................and yes, in a jacked up, big tired, 2wd Jeep