96 Mustang GT 4.6 PI conversion tune up questions

Hey guys~

I am usually on the 5.0 side but I do have a 96 GT with PI conversion done(Parkway performance Kit), I did this about 4 years ago and it has been running fine ever since. Now the time has to come to do some tune up and upgrades such as headers and etc, etc

My questions is:

1. What kind of spark plug do i use on these now? Do i use the the 2004GT spark plugs or the 96GT spark plugs?

2. I left the stock 96GT headers on the PI heads because i was broke after the swap, Do i need to upgrade this to ford racing or aftermarket ones? I heard the port shape is different between Non-PI and PI...so i should get 99-up GT headers?

3. Do i buy 96-98 aftermarket H-pipe and performance exhaust or 99-04 H-Pipe and aftermarket exhaust?

4. What is good Mod for a street car like this? The plenum and throttle body, intake manifold is all stock, Would i see some good gains with just changing those out to aftermarket piece? I was thinking bullitt intake and TB swap or trickflow intake swap along with TB?

My girlfriend drives this car so i can't cam it or supercharge it or anything,,,It is going to stay N/A...sad i know...

I feel like a newbie asking these questions but I rather ask before i do something stupid or buy something that is not worth it, I am kind of new to 4.6 stuff and still learning

If you guys would let me know about these that will be awesome!

Thanks
Leo

Any one else? Need more opinion on intake and TB set up!
Thanks

Thanks all for the good advice~

I got all the suspension pieces together and i already started to put things together, Sub frame connectors, Upper and lower control arms, springs, shocks & struts, and H-Pipe, FR500 wheels from my 95, My girlfriend wants to keep the back seats.

As far as exhaust i think i should keep the stock shorty headers for now until budget allows for long tube? People are against the shorty since it really doesn't improve any performance? I already have the H-Pipe for the shorty so i was thinking about putting that on for now...

As far as intake should i keep the stock one for now or go aftermarket? I have no desire to put blower or shot on this car, it will stay N/A, If i go Trick-Flow intake set up along with TB(what size?) will this help on top end?

I fully understand about the typhoon intake, i won't buy it.

Let me know and thanks all