Having welded in the passenger side firewall extension (toe board), it came time to install the driver's side. The driver's side is a bit more confined and thus difficult because of a the obstacles of a fresh air vent and the steering column. I began by marking the approximately squared off patch location that would A) remove all of the rusted, jagged remaining metal and, B) preserve the odd oblong hole in the original toe board just below the steering column for the emergency brake cable. The aftermarket firewall extension didn't have this hole and the steering column indention was of the wrong shape so I opted to try to preserve both since the metal wasn't rusted out in these areas:
Here's the replacement patch as received from NPD minus the red primer. I reused my template from the passenger side inner rocker and marked the driver's side inner rocker and some welding tabs. There's a lot wrong with this panel such as incorrectly shaped driver column indention, missing speedometer cable hole, missing cut-out for convertible inner rocker, and the outside flange is bent down instead of up which interferes with the inner rocker.
This is after I cut out the shape of the patch that I needed, cut out the inner rocker notch with tabs, and bent the outside flange upward. After I cut this panel out, I then overlaid it into position over the old driver's side toe board, torque box, etc. and marked the car to match this patch instead of the other way around as I did on the passenger side. I then cut the original toe board to match this patch. It seems to match the cut-out much better using this technique than the passenger side did.
I test fitted the patch in position and marked from beneath the car, the location of the torque box and frame rail flanges so that I could mark the plug weld holes. The diagnol line represents an angular indention on the torque box inner panel (see first picture) and I had to be careful not to position a plug weld hole along that line. This is a view from the bottom of the patch panel with dots indicated plug weld hole positions.
I then drilled all of the plug weld holes and ground the primer off of the edge that would be mated along the butt weld line for placement against the hole cut out in the driver's side toe board. This is what the prepared patch looked like just before installation.
Finally I could move onto welding the patch in by seam welding the butt joint and plug welding to the torque box and frame rail flanges. You can see the self-tapping sheet metal screws that I used to pull the patch panel against the torque box and frame rail so that there's no space between. The screws were removed soon after this shot and the holes welded closed. Note in this image that the steering column has been removed. This allowed me much more room and comfort for completing this task. Using an air wrench, it only took about 15 minutes to pull the steering column.
Lastly, I ground down the welds with my 4.5" angle grinder, filled some pin-holes and smoothed it all up with a flap disk. There's a little more patching and clean-up to do for both firewall extensions but that will be done after I remove the remaining floor and tunnel which will be my next task in preparation for a new full-size floor which I'll be ordering shortly.