If you after these in a hurry call Hi Octane Racing for all the Tomei stuff (they deliver overnight), get CAS (local) dumps instead of HKS ones - I have Wiseco pistons in mine but there are heaps of other brands available. If price is an issue then use Nengun but you may be up for a wait.
My pair of HKS 2530s each needed a restrictor however these were older units, not the GT series like yours - GCGs advice supports what the other guys have said above ie you do not need a restrictor on the GT series.
Guys, (not wanting to spark the my oil is better than your oil debate!!) I was speaking to the owner of one of Brisbane's largest tuning shops & it was interesting to hear his feedback on a number 8-900hp Jap powered drag engines that had been pulled down - bearings didn't last long on Motul (not the 300V Chrono), even less on Mobil 1 - recommended Castrol R.
Current version, hand controller, new in box, suit BNR32/R33 - SOLD
Z32 AFMs x 2 including plugs & air filter attachments - both checked & recently cleaned (good working order), will separate - SOLD
Brisbane.
Pm if interested.
Without a restrictor the turbo gets too much oil, which at high revs/boost forces oil down past the seals which gives you a smokey exhaust. This happened to mine at over 5000rpm using only 0.6 bar boost.
Guys, when upgrading from plain bearing turbos to ball bearing ones make sure either yourself/mechanic installs oil restrictors in the oil supply lines, you can get these from GCG - HKS kits will inculde these but most ones purchased second hand will not.
Definitely go modded provided you get it checked out by a specialist. While it may be fun doing the mods yourself, you'll be digging deep into your pockets if you go down this track not to mention having your car off the road for a considerable period of time. I've just been down this route & if I had my time over again I would have bought a modded one & saved heaps of $$.