There are alot of forums on here covering all R32 GTR's.. including Vspec, Vspec2, N1 and Nismo.
Just do a search and u will find what u looking for. There has been some really good info posted over last month, should be easy to find.
Yes only 500 or so were made.. If they are genuine Nismo, they would probably have been given a work out, and i think the earliest nismo's were released in 1990.. just off the top of my head. I definately know they have a body kit, inlcuding side skirts and a small rear spoiler lip.. also common on N1 R32 GTRs, also and option for a bonnet splitter that forces air to the radiator.
Hope this helps
Cheers