My 83 is rusted in a similar way, though not as bad. It’s weird because like yours the sill is near perfect. If you are going to drive it like that make sure the structure that supports the tire carrier is solid
You can get replacement panels for those sections, or at least the PO of mine was able to get them at some point.
View attachment 2775462
Is this 1983 a US spec vehicle ? If it is, it is pretty rare.