Would this be a deal breaker?

Yea once you start digging I have a feeling that car is going to be a nightmare. Of course it could be done. Price out all the necessary sheet metal you will need from AMD and see where you are at, at that point. For 5,500 he's real proud of that car. If it had the original 340 then yea it would be more worth it. Get a screw driver and poke the **** out of that car everywhere. The trunk floors are probably shot even if you can't tell exactly where. If the car runs and drives, find a place that has a lift give them 20 bucks to put it on there for 30 min and really go through it.