this
http://www.aaroncake.net/RX-7/buy2.htm
and the basics like coolant color. oil color and smell, tho the oil on these things smell funky even if its fairly fresh. Oil pressure oil PRESSURE! check also for visible leaks or any sings of oil leaks. and also make sure the diff mount is good, you'll quickly find out through a test drive, if its bad or torn or w/e ull hear a loud thud every time u shift or engage or something.
even if everything checks out fine tho, ur still most likely going to put money into it just to maintain. Good Luck