Auto body repair & detailing: Body Mount Bushings, rectangle piece, malibu ss

Question
Can I change the body mounts without taking the body off the frame on a 65 Malibu SS. I only know of one broken/rusted bolt. The others seem ok just 40+ years old. I do realize the two over the rear tires might not be able to change the top rubber.One last thing where are the nuts? Welded to the floor? Are there openings under the carpet to get to them ?????? Any info would be great THANKS

Answer
You will probably have to cut holes in the floor where the nuts are. You should see a bump about 2" in diameter and about 3/8" high. They are not normal nuts, it will be a square or rectangle piece of metal threaded for the body bolt. Cut a large enough hole to get to it, at least a couple inches.