The frame might not be bad. Sometimes these cars can have extensive body rot but the frame ends up being clean. On the other hand, cars that have great low mileage bodies that have nice shiny original paint might have a frame that is completely shot. You can get replacement rear frame rails to fix it though.
http://www3.sympatico.ca/conradlozier/
http://www3.sympatico.ca/conradlozier/