I like the rivet nut idea. It's a little hard to tack weld a nut on the inside of that location due to the location of the rear fender support. I'll have to look for the rivet nuts.
Before my next task, I took some time to read over Guys Resto thread. I opted to use his method for installing the back floor panel.
By the way, I ordered the panel on Weds, and it got here Friday. Upstate NY to Florida in 2 days.
I spent several hours installing the new back floor panel from CMD. I drilled the frame and welded from the bottom. I painted all surfaces with POR15 (which should be renamed POR $150). I also marked the locations of the welds, and sanded off the coating. I positioned the panel, and fixed the location with two self taping screws. Then flipped it on the rotisserie and positioned the lift under the upside down body. I used the back two lift arms to locate 4X4s strategically to press upwards on the panel when the lift is activated. I had to keep moving it to get pressure at the locations for the welds, but this technique worked really well to press the panel tightly to the frame as I welded it in location. The floor is very flat and tightly in position. It came out a lot better than my previous attempt on the 64 M151.


Sorry, forgot to take finished pics before I left the garage.....