While I've never owned one, I my brothers close friend did and I own several older cars. So, I'll chime in. Basically what I tell anyone who asks me about an older car is that you need to have the body checked out. Those Datsun / Nissans would rust rather quickly compared to cars that were from the US or Europe. My brothers friend LOVED the powertrain in his, but hated the body. In the old car world, there is a saying that white hides all sin. IOW: Painting a car in gloss black would show most every defect while white helps to not highlight imperfections. If you are serious about wanting the car, bring it to a body shop and have someone look at it. Hopefully you know someone a body shop but even if you don't, be sure to make it clear that you will be paying 1/2 - 1 hour of labor rate for someone to inspect this car. A hundred bucks now could save you MUCH more later. Think of it this way: Whatever defects are found will tell you to walk away or SERIOUSLY improve your chances at negotiating the car to its proper value. It is entirely possible to look at a $5k car and buy it for $2k or $3k once you know what you are getting into.
When I bought my '72 1800ES, I asked the seller where was the closest repair shop he would bring the car to. I went over there and set up with the manager / owner 1/2 hour of lift time for (IIRC) $30 or $40. I knew that getting into a uni-body car that had underlying issues would have been a nightmare. The guys in the shop were great and after they raised the car loaned me a droplight and were eager to take a peek underneath the car also. I was able to look for fuel leaks, oil leaks, trans leaks, rot, rust, evidence of previous accidents / repairs, recent repairs (obviously new / newer parts), etc...
Now here is the interesting part: from what I understand Nissan didn't produce any 2000 Z cars. They were retooling, so 1999 was the last car until 2001 or 2002. IIRC, they restored a slew of Nissan Z's and sold those until the new cars came out in order to ressurect interest in the car and fill in the gap in their lineup. I remember hearing about it because for $20k you were getting a factory restored car. I remember hearing how it affected the pricing on other Z's that were already restored.
EDIT: Does anyone remember hearing that Nissan restored a bunch of first gen Z's (240's?) and sold them in showrooms to cover the gap for the 2000 model year when there was no Z?
Edit #2: The Datsuns didn't use a real 'Skinners Union' SU. But a Japanese equivalant made by Hitachi (the needles are the only part that would interchange). And for what it is worth, a SU is one of the simplest carbs for an automotive application on the planet. Most people blame the carbs rather than the real engine or ignition culprit.