Decided to cut away the strip of the boot pan I had previously left on top of the box section. I would not be able to weld to it, like I had originally planned, it is of too bad a condition. I had concerns about it providing structure to the box section, but now think it is strong enough and is supported at either end to under the body and to the tail panel.
I also cut away the remainder of the pan to the right, fully removed the wheelhouses (just a case of finding the spot welds) from the rocker panel and tidied up some previous cuts. Just need to work out what to do with the shock mounts and then clean everything up.
A professional sand blast job is very appealing and seemingly a necessity. The entire rear end, bulk head, interior needs to be removed of rust, and there are too many awkward surfaces for a wire wheel or flap disc to do a satisfactory job. My new shot blast gun and 11cfm compressor is still not up to the job (to small a blast diameter, and not enough force behind the grit to remove dirt let alone rust and layers of paint).