floorboard question

Get the replacement parts(s) first. It will guide you on what has to be done.
I did this on a 69 cuda. Once the carpet, seats, console etc. are out, remove the sheet metal wireway by the door opening and drill the spotwelds that attach the floor to the frame rails and the top of the rocker panel. Drill the spotwelds at the pinch weld in the front and make a cut front-to-rear along the hump. I also had to cut side-to-side where the front joined the rear floor because I only did the fronts.

It's pretty self explanatory as long as you have the replacement(s) in hand and a bare floor to look at. Don't cut anything until you get the parts just to make sure they will cover the whole area.