My Dynomax cat-back is a 99-01 part number so there shouldn't be a problem in the case of your Flowmaster system. I think the only difference in the exhaust systems are the exhaust ports. (03's are shaped differently).
Hey TETGE....I am not exactly sure on the Part # but I had UPR Products install an off-road x-pipe with the Dual Chamber Flowmasters and I LOVE LOVE LOVE the set-up. It sounds incredible. Of course one will always be partial to one's own car but I think it sounds better then any other set-up I have heard. Black03 would agree with me on that although his sounds mean also
Mine bolted right up, sounds great, I love it (even if it cost me a couple of "pound-feet"...). :-D My dyno numbers were 1,200 miles with K&N drop in_sans silencer and the 17248 on stock H (put on the day before).
Flowmaster American Thunder 2.50" Exhaust Kit is listed in the FAQ and here: <http://www.rpmoutlet.com/mus03flow.htm>. I thought you were going to leave your car stock!?