The 1998 cobra exhaust will NOT fit the 2003. The main difference is the way the pipes are routed around the solid axle in the 98, while the 2003 has its exaust underneath the IRS.
Is it just the cat-back that is routed differently. or does it effect the h-pipe? I know the 98 h-pipe will clear the t-56!!! I am going to use the h-pipe from a 98 with the cats removed of course!! I am then going to weld exhaust piping inside the converter housing to take care of any tin sounding noises. I will already have the cat-back that came with the 03. It should hook up to the h/pipe with ease. if it doesn't.... oh well, I love a challenge!!!