At the end of my last entry, I had marked the positions of the plug weld holes and had drilled the holes through the floor so that I could weld down into the new lower seat reinforcements.
The next step was to re-fit the new metal to the underside of the floor using the alignment marks I had previously drawn. The left and right lower seat reinforcement panels were installed together at the same time joined by the tunnel reinforcement plate. The through-hole clamps were inserted into seat track access holes and tightened up. I then drilled 1/8" holes into centers of the 3/8" holes at the ends of each reinforcement flange and inserted the Clecos that had proven so useful during the floor installation stage. The Clecos were drawn up tight such that I really didn't need the bolts in the seat track access holes anymore but I left them for good measure. I also installed clecos along the panel flange that contacts the inner rocker on the underside of the floor.
The final preparation step before welding was to use a flat-end spot weld bit to expose fresh metal on the reinforcement panel flanges through the plug weld holes.
Finally, I could begin welding. I welded each of the holes in a kind of alternating pattern, like you would use to torque wheel or cylinder head bolts. It's probably not necessary but my gut feels that it helps with heat distribution. I've been using similar plug welding patterns throughout the car.
On the underside, I seam-welded the ends of the front floor reinforcements (frame rail extensions) to the new lower seat reinforcement panels...
... and welded along the bottom of the inner rocker.
I ground the welds on top first using the course grinding wheel and then moving to the 60 grit flap disc. Since the seat pedestal is going to cover this area, I needed to grind the plug welds flush but there's really not a need to make it smooth... well, I guess that technically there's no reason to make any of the floor pretty because it's all going to be covered by carpet but dammit, I just can't help myself.
Finally, I ground down the welds on the lower part of the inner rocker because they will be seen by brake, muffler, and oil change guys and do I really want THEM to think I can't make a pretty plug weld? Hmm? I think not.