Get rid of the BOSCH JUNK. Nissan's engineers designed you engine (and all of their engines for that matter) to run on real plugs. NGK is the only plug I will use in any car I touch. I tried the bosch plats in my Z32TT. I installed them, drove around the block and felt a noticable "seat of the pants" difference, THE WRONG WAY. I pulled the 300 right back in the garage and put the old plugs back in for another 20k miles.
I had Denso-Rs in the NSX, but I like the NGK-Rs in there too (Same plug as Z32nonturbo) Nissan gives ne wholesale at the parts counter. $6.50 a plug. Most guys will discount you too if you are cool with them. Go with what works! NGK.
Air in is good.
AFM - Z31 60mm
TB - KA24 60mm (match the manifold AND the edge of the TB to the NEW gasket) Be sure not to grind the part where the butterfly seats, though - very bad.
Plumbing - good luck if you keep the AC. Get it away from the exhaust. Get someone (some exhaust shops can do it) to make you an intake pipe (60mm hopefully) and "squeeze it past the AC"
Air out is good (but not too much)
I used Z31 headders from Pace Setter and "massaged" the fire wall abit (read: 12 lb sledge hammer) I can "heel toe" the pedals alot easier now, but I wouldn't do it again. Find someone to fabricate it for you. I am going to have mine re-done, because the pace setters rusted to crap within a year - Junk!
Do you have emissions there, if no STRAIGHT PIPE, If yes, high flow cat.
Cat back (you already have, right?
Fuel, While you have your manifold off to port match it to the TB, have the injectors checked. Any good diesel, big truck, or turbo shop will clean and flow test your injectors for about $15 a piece. MONEY WELL SPENT.
Spark, Upgrade your coil and use good plugs, NGK. I like the heat range 6 short electrode NGK-R. (Same plug from Z32nonturbo (VG30DE). Check wires, use an ohmmeter. If any are shot - replace them all. The others will be soon to fail. Stock wires are OK, I made mine from a V8 Excell 8mm custom "cut your own length" kit, but mainly because they are yellow and it looked cool with the dark metallic red paint.
Free up power by getting rid of the stock fan and clutch. The less power wasted on that stuff, the more power to the wheels. You can get bigger pulleys for alt, pws, and AC, but DO NOT TOUCH CRANK PULLEY. The VG series engines produce harmonics at 2 different engine speeds, the stock crank pulley balances them out, take it from me, underdrive crank pully = bearing failures.
From there, DRY NOS or water injection. DO NOT SPRAY WET NOS IN THE MANIFOLD, the gas collects on the walls of the bends in the manifold and that means it does not get to the cylinders. If you want big nos, do direct port, or change the injectors to larger ones, and do custom fuel mgmt, again, take my word for it.
That is all of the "little" stuff. From there you start getting into big $ and losing reliability. Plus, you can get a DETT for $2500 with trans, or a RB26TT for less then 4 large, so why waste time on anything else?