Honestly, I would stay away from GSRs; I know too many people who has had their's stolen and it is damn near commonplace.

300ZXs are extremely hard to find in decent shape in my parts; most of the to-be-sold 300ZXs around here usually have 125,000 miles and they are hardly in good condition. The lowest one I found was around 75,000 miles, but it was the NA version.

I would honestly try to find a 240SX if I were you. Like Mike (MrFatBooty) said, it is not impressive with the KA24 (155HP) until you get the SR20DET (220HP, turbocharged). Not to mention that you would not have to worry too much about the internals unless you are seriously going to boost it a hell lot. SR20DET have insanely beefy internals as is.