What to look for??
First, take a close up picture of the fender tag and get it decoded. If you post the numbers on FABO someone will decode for you, or you can download free fendertag decoders off of the web.
Second, crawl underneath and check floors and frame rail for rot. Also, check VIN on trans and motor to see if it matches fendertag and dash VIN.
Lastly, take a thin magnet to check for filler in the body. I use those thin realestate broker fridge magnets. You can cut them into small pieces that are great for checking for body filler.
What's the asking price? Is it an original 340 numbers matching car?