You can see here where I cut the metal beside the back support. The one under the back seat. I saved this piece of metal for a template for a new piece, to give me a rough idea on size.
I am going to pull this floor support out because of rust between the support and the rocker panel. Then I will put a new piece of metal in and butt weld it to the original floor and new pans. Then plug weld it to the support.
I want to show you the gap between the rocker panel and the floor pan. On drawing number 6, I said that this gap is 3/16 up to 1/4" wide. I will weld that gap solid the full length of the rocker panel.
On this picture you will see the new floor pan overtop of the rocker flange. That hole looks about the size of a nickel or a quarter, the black you see in that hole is the lip of the new floor pan. This is to give you an idea of how much of the floor pan is down inside the rocker panel.
This is just an underside view of where I cut beside the support.