You don't need to do PI heads unless you just want to. You can get very close if you do
Your current heads (can run a much bigger cam in NPI heads than you can in PI heads without notching the pistons)
PI intake or better (the better the intake of course more power)
Some MHS NPI cams stage 2 or bigger depending on your budget.
+ the standard rest of bolt ons.
This way saves you from ripping apart the engine completely. Just a cam swap (maybe spings depending on cam selection) with an intake. Plus a tune of course.
I'm assuming you have basic bolt onts already.
My 96Gt currently has basic bolt ons and the PI intake. It is so much better than before. Come spring I'm tearing it down and doing some Cobra flat tops to bump compression, and basically what I posted above. Should see good results. I may switch it to the edelbrock intake though. Haven't decided.
Anyway, check this link out. The NPI heads were not the 96-98 2v's problem. Crappy cam/intake were.
http://modularheadshop.com/Articles/11secondnpi.htm
You don't have to tear the motor down to get close if you choose your parts wisely.
If you get MHS cams you can have them degree them before they ship them to you and you can just line the dots up and go.