the xaust ports are the same on the PI and NPI heads. get the 98's b/c they will hook to the rest of your xaust system w/o any (well I can't say it will be easy) complications. The 03's may not
p.s. I wish I had wraped my headers with heat tape or some other heat sheild b4 I installed them.
The difference is in the exhaust pipes, not the ports on the heads. Nothing changed considering the angle or distance of the exhaust ports, and most importantly the exhaust manifold bolt locations. You buy the exhaust for the year of the car in this case so you'd buy the headers for the year of car also.
Yes, I do have the FRPP headers. They will help and improve, but not like longtubes. If you have no issues with emissions, ground clearance, etc., I'd suggest you go with longtubes or even JBA shorties. But if you already own the FRPP headers, go for it and don't look back.