The resulting part looks like swiss cheese:
I test-fitted the floor support to the frame rail, marked the hole locations, and then used a flat ended spot weld bit to expose a 3/8" circle of bare, clean metal to weld to as shown in the image below.
The area is doused with Ospho, rinsed, and scoured to neutralize the rust.
A view of the front portion of the inner rocker after cleanup.
Everything that harbored surface rust within the vicinity of the inner rocker was given a coat of ZeroRust encapsulator to seal it up in the event that moisture ever contacted the area in the future.
A view of the front portion of the outer rocker after ZeroRust is applied.
The driver's side of the car is now ready to install the torque box and inner rocker panels. This is a shot of an initial test fit. The torque box needs some adjustment as it doesn't fit quite perfectly. After I do that, it's time to weld and then the car will once again be structurally sound.