Thick,
From viewing this pic, I am fairly sure the previously mentioned "rocker panel" patch noted will work to provide a replacement "section" for that partial rocker panel area you have circled.
The primary shape of the rocker panels, as well as the width of that sill area, should be very nearly identical.
Just note that you can trim out the section to be patched and replace it with a same sized section from the patch panel, without having to replace the hole length of the rocker panel.
Much easier this way, plus removing such a small section should not compromise the structure. Should be minimal need for bracing of the entire door opening as you would have to do if you are replacing the whole rocker.
Also fairly sure you can find/order just a drivers side rocker panel patch without having to buy the whole kit.
For more info and other posts about doing such cab patch work, take a look in
The Paint and Body Shop forumYou may want to ask additional questions there as what you are preparing to do falls right into that category perfectly.
Good luck and let us know how things progress!
