Floor Pan Install Question

Sawzall's don't seem to work very well for me. I have one along with a 41/2" grinder/cuttoff wheels and a plasma cutter. I was thinking drill all the spot welds and cut the old pan out smaller than the new pan. Then laying the new pan in and using the plasma to cut the new pan along the edge and the rest of the old pan out at the same time. Butt weld or stich weld it in. What about the folded front seam??? Leave it there and cut it out say an inch below the folded seam??????