I have a 99 I/S and when I did the nut cage mod it was similar and very easy. I used a Dremel tool to cut the cage and then grind down the welds. Be careful not to get it too hot or you will ruin the paint.
I used the same bolt. I ground the hex head down so it looked like a carriage bolt, painted the head so it won't rust. I installed it from the inside out and used an acorn nut on the outside. Worked fine.
If you don't have an acorn nut handy, used one from each side of the rear muffler hanger. There's a total of four there, so you'll be OK untill you find replacements.
