Here's a shot of it after I had cut out the rusted section and removed the seat belt captive nut plate.
I cut out 14 gauge sheet metal patch that fills the area I had removed.
I welded the patch to the brace from the inside so the welds wouldn't show from the outside.
I then welded a strip of 14 gauge sheet metal to the outside edge to replace the rusted-away flange, and ground it smooth.
After I had welded the seat belt mounting plate back into the brace, I welded it and the A-shaped brace back into the passenger side of the car.