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I wouldn't port the heads...the heads on this motor are great.
I would do:
Test pipes (non-resonated if you can stand the rasp, you'll gain more power with non-resonated than resonated)
ProFlow or 350EVO throttle body (350EVO's throttle body work is done by ProFlow, but 350EVO offers a core exchange to prevent downtime, Proflow's is a little cheaper due to no core exchange, ProFlow bores it out and polishes the throttle body plate)
Cat-back exhaust...I suggest Borla (deepest sound I have ever heard for an exhaust for the 350Z), Injen (sounds ricey IMO), or Stillen (sounds pretty deep), all of these claim the highest gains, all are dual exhausts, Injen is the only true dual out of those though; if you are going custom, I would say this is up to your friend. Personally, I would go with 2.75" (mandrel-bent) titanium tubing with either two HKS Ti (or Carbon Ti) mufflers (true-dual) or one HKS Ti (or Carbon Ti) muffler (you would use a y-pipe for this)
KJR Performance crankshaft pulley (stock size, but it is lighter), gains about 4hp (not bad for a crank pulley)
Altered Atmosphere ECU reflash - $495 I believe
Intake manifold/intake plenums: I would wait and see what Kinetix's intake manifold does, but right now it looks like the gains are pretty crappy for the price, not to mention they aren't great for F/I either at that price, we'll see though. 350EVO plans on making one, which means it will be geared towards N/A...so you'll see much better gains from that. Also, another company that is reputible is coming out with an intake manifold and it should be promising as most of their products are. If you don't want to go with a intake manifold...I would go with either a Crawford cast upper intake plenum and Nissan OEM 300HP model lower plenum or plenum spacer (AAM or Motordyne Engineering) and Nissan OEM 300HP model lower plenum. (or even an APS upper intake plenum + Nissan OEM 300HP model lower plenum)
This depends on if you plan on going F/I or not...if you are staying N/A or have some extra money...I would get an Injen cold-air intake. If you are going F/I, I wouldn't bother touching the stock intake
Some other things that I think are interesting performance mods (not necessarily power, but helps the power:weight ratio by weighing less and/or transferring weight or cooling the engine better)
Motordyne Engineering hood spacer (this decreases engine temperatures all around the engine by 45 to 50 degrees F...should be good for the track days to help stay cool and prevent heat soak from happening sooner
Odyssey PC680MJT battery, weighs less than stock and won't decrease the performance of the battery; mount this battery in this:
Moroso battery box and use these cables to mount it behind the drivers seat in that compartment:
Moroso battery cable kit
Moroso fuel cool can. For every 10 degrees you cool your fuel, you gain 2-4%hp...I figure to mount it where the stock battery used to be and use:
Summit Racing 2' fuel line and get some fittings for it and you should be set, just run the lines that go to the fuel rails and run them to the fuel cool can and then run the new lines to the fuel rails
Other things are removing the rear wiper and motor. Also, going to lighter wheels would help. I can't think of any other mods that would benefit you vs. the cost.