Not too familiar with AD but I don't see any "interior" rust out. Try to stick to the rule of only replacing rust, not a whole panel.... except where it is necessary to cut a little more to attach a patch using a more practical/favorable method. I.E. land on a ledge/spot weld flange/access for welding/backer.
At least one of your pics shows a pillar/hinge pocket not a cowl.
Interior light or heavy surface rust can be: reach-in spot blasted, wire wheeled or just scraped. Vacuumed. Then apply Rustoleum Reformer spay-on or Ospho or any type converter or encapsulator you like. That's exactly what those products are for.
Read allI would just make a flat patch for that pillar using a left over piece from some other patch. I would use a thick used grinder wheel to round out that bad welded inside corner radius.
But most of this is from just seeing a few pics from a far away place. Your informed judgment is best. Many other members here with patch experience.
