id have to disagree about the better gaskets for less money. the genuine nissan ones are pretty good and on most of the cars have lasted over 15 years before failing.
nice work on the reformat.
you may have just lucked out with the combination of your injector size and Z32. the Z32 with standard injectors will make it run lean, the injectors with standard AFM will make it run rich.
R31 nismoid is making around 300kw and has a legal exhaust, my car is 92db and makes over 300kw.
ask an exhaust place to make you up an exhaust with the biggest straight through mufflers they can fit.
topics been done to death.
they are slow but you will get your stuff. check out http://greenline.jp/ or http://www.rhdjapan.com/ if you want faster service