Bill, yes the floor panel was plug and stitch brazed in with the plugs matching the original spot weld locations. In this application a brazed joint or plug is as strong or stronger then a spot or MIG plug weld. The reason is the bronze will weep between the two pieces of metal binding it to a larger area then a weld will.
When I started this project I got all excited about the new goodies I could buy. A TIG was not in the budget, a good MIG was attainable, and a spot welder would have been neat. Then I looked around. In my tool inventory was a sputter box and oxy/acet torches and the such. I knew how to gas weld and braze. So, rather then buy additional equipment, which I would have had to learn how to use, I decided to go with what I had.
The first floor I put in I stitched gas welded and brazed. When I did the rockers, after researching and discussing with professional welders, I went with the brazing and have been a happy camper. Goes fast with little warping. The only extra work is getting the flux off the weld. But then I do not have to grind.
Oh, and before I opted to braze I did a destructive test on a plug weld, a spot weld, and a brazed plug weld. To my surprise, the brazed plug weld was the hardest to pull apart.
Oh, the only down side to brazing is the flame. Care does need to be taken not to scorch your body or burn down the shop.
I also have used the oxy/acet for panel body work, bumper repair, and many more things.
So, while brazing may not be for everyone, but it works well for me.
I do envy you and your plasma cutter....