I don't recall noticing that, but on mine a couple inches of each lower corner does curve inward very slightly, then goes pretty flat for the remainder of the exterior surface.

The inward curve is enough to require a flex block in that area.

The originals were somewhat like that too, but admittedly I may have changed it slightly when I did the rust repair to the structures.

Both door jambs are now stripped/epoxy/surfacer @220 following same process as the rest of the body, behind the A pillar bulkhead seam.
To complete the jambs and bulkhead in front of the A pillar seam the car will need to be disassembled more/dash will need to come out, which will come later.

Left rocker panel and pinchweld strip/prep/epoxy was last night. The quarter to rocker transition fill has been roughed in lead for some time, I will finish it in polyester tonight or maybe tomorrow.

I use tall jackstands when I need extra room to work, to get the hoist arms out of the way and allow me to work fairly comfortably standing up.