So we got after that rust. Welded in ( poorly, because I’m not a welder ) patches where necessary with some 20ga sheet metal. I didn’t happen to have a thickness gauge handy but it was actually stamped on the steps on the body. And sure enough it matched right up.
Then we wire wheeled that all down and hit the spots with some Rust Reformer.
Next we cut fur strips out of 3/8 plywood to go over the floor to kind of smooth things out. The plan is to not actually drill into the floor pan given the age and potential for rust we wanted to limit the amount of entry points. We’ll be using some adhesive to hold the floor down.