RJ, I think you'll find that most cars are spot welded together. This is a very old technology and works very well. The only seams that were welded full on the 122 were the door window frames, the seam at the top of the C-Pillar, the front and rear edge of the sides of the hood...that's pretty much it. The rest will all be spot welded.

On the removal side of things, if the floor panels are rust, cutting the spot welds out is a waste of time. Just use a cut disk on a grinder and knock it out of there. The cutters that George and Cameron mention are fine, but unless I need to keep a panel intact, I've found that it is just easier to cut them out and grind the overlap off.

After I have the panel off, I use a 1/4" punch to pop holes in the new panel, then button weld it in place. Looks like a spot weld and works great. Every panel that has been welded should be seam sealed. Don't forget to clean off the oils on the sheet metal first.

Craig