Before I explain my pictures, there is something I need to mention. I put these pictures on four forums, and I get questions now and then. I'm going to take the time to answer those questions as I go along, so you'll see me throw an answer in once in a while. We need to keep in mind that these pictures are geared for beginners as well as those who think they know what they are doing already like me.
You need to take the burrs off the edges where you made your cuts. I use a flat file and a pair of cotton gloves. Take the burrs off both sides of the pan. You can feel them with your cotton gloves. Don't do any filing on the flat edge of it, that can be a little rough but that doesn't matter. A couple of sheet metal screws beside of the weld will keep that gap. The only thing you need to concentrate on is the up and down of the pans lining up for butt welding. Take that file and de-burr the toe board area on the body also.
Had a question about cleco fasteners. I used these when I lapped the metal on the toe boards, but I wouldn't use them on pans because they won't draw down like a screw will.
In this picture you can see where I squeezed the fastener with the cleco pliers. When you squeeze them it extends the tips and if you drill a 1/8 hole in your sheet metal pieces you can insert that into the holes then release it and the tips expand to hold the two pieces of sheet metal together. The tip expanded is .170 and 1/8 of an inch is .125.
A picture of two pieces of sheet metal with a 1/8" hole in them.
Factory spot welds are usually 2-3 inches apart when you're dealing with trunk and floor pans. I took a tape measure and put 2-1/4" marks on the rocker panel, then I stuck the floor pans in, put a couple of screws in it, then extended that line across the edge of the pan.