There is a very small step that needs to be machined into the stock flywheel, it makes a big difference. Not sure how this applies to the the Fidanza.
did you replace the clutch cable? if so, was it with a GENUINE NISSAN cable? If not, I can almost guarantee this is the problem. Generic cables are PURE CRAP and usually cause all sorts of adjustment issues.
You may want to make a small spacer for the clutch cable also, this can help a lot with adjustment, but with a genuine nissan cable you should have no problem.
Redline MT-90 made the synchros function far better on my old tranny and eliminated any grinding when slipping into gear.