Well, I just got off the phone with my body guy and he says that the cage nuts I got from
http://www.SS396.com are good replacements for the ones under my trunk floor. So my previous post was in error.
Bad65, I had to cut into the trunk floor from the top to get to the nut. I took an air chisel and cut a three sided flap in the trunk floor and pulled the flap up. I took measurements from underneath the car to try to pinpoint where the nut was located, but when I first cut the flap I was off by about three inches too far to the outside of the car. So I had to widen the flap by about two more inches. As soon as I rolled the flap back I was able to see the nut. I then just put a pair of vice grips on it and then un-did the bolt from the bottom. My body guy says he will be able to fold the flap back down and weld it up and when he's done you won't even be able to see where the flap was located. We'll see. But he's done some pretty incredible metal work for me before, so I have confidence in what he's saying.