Overheating could be as simple as an airlock in the system. I’d have it sniff tested. Who was it’s last owner or was it from a garage? As for the rust put some pics on. If I had some of the underneath of mine when I bought it I’d put them on. It had overall body corrosion as an advisory on mine 2 years ago and I got rid of that last year. It took a good few hours, a wire brush, some rust treatment, and paint. I could of undersealed it but it’s only out in the summer so there was no need.