Can't answer you until you tell me more...
1) What are you going to use the car for? Daily driver? Weekend toy?
2) Is it a straight trade, or cash difference? How much, which way, etc.
3) Like StangGT1995 said, is it really "clean"? Check the floors, rear frame rails and torque boxes, trunk drops, inner fender aprons, rear quarters for rust (or bondo repair).
4) Have you driven it? Are you happy with the way it drives? I much prefer 1st Gen stangs to Fox bodies, but there's a world of difference in how they drive out.
5) Is it front drum brakes? If you haven't experienced brake fade with front drums, take it for a test drive, warm them up real good, then do an urgent stop--just make sure you've got room on both sides when you do!
If you're asking "what's it worth?", we need to see pics, and know more about the car. If you're asking "what should I do?", only you can really answer that. We can help you by telling you the +/- of a vintage (I assume you know them for your car), but in the end, you gotta decide what will make you happy.