Help -Blank door removal

[Franks 72]

I need advice on replacing the inner floor extensions (or sil backing plate) behind the forth (blank) door. I have removed the bolts which pass up through the floor and into the door frame , the large screw heads which secure it to the pillar and drilled spot welds in the rear portion of the false door. My question is ,are there additional spot welds hidden under the rear window inner support. I would rather not remove it. Should I cut the inner door or access from the outside? Also does anyone make a patch for the second cab support (see photo)
Thanks for your help !