After a lot of contemplation I finally committed to pulling up the whole cargo floor area. This was not a decision taken likely, many hours staring at the rust and the calculating how may repair patches would be needed in that corrugated floor, and how impressed I was with the replacement floors produced from Muscle Bus, finally got me to the decision to attack the many spot welds that pin this floor down. Once I started I knew I had made the right decision. I just hope I don't regret it later.
I could have attacked the floor slicing it to pieces with a cutting disc along the edges of the outriggers which would have been fun but I felt I wanted some sort of recovery plan if I did make a huge balls up. So I decided to take the floor up in one piece, this meant removing every single spot weld. Although I had a spot weld drill I found it better to start with a sharp 1/8" drill bit carefully cutting only through the first piece of floor then finishing with a 3/16" that I'd slightly ground the tip flat so that it cut no further than the depth of the first drill bit. I only slipped through both pieces on a few holes and my knees suffered for too long on the ridges of the cargo floor.