This is a good place to start:
http://www.gnttype.org/general/buyguide.html
Having someone knowledgeable with you would be of benefit.
Since these cars are getting older, many of them have had a lot of hacking and bad work done on them. Best to find one that has been with an owner a long time and treated well, modifications or not. When they get into the hands of those who don't know how to work on them, things can get messed up quick.