Floor Pan Install Question

I wouldn't use a reciprocating saw for floor pans.You can pick up a body saw or a cutoff wheel/grinder to cut the floor. The body saw has a real thin blade therefore less gap. Cut the new pan to the size needed. Screw it to the old pan and cut around the new pan as close as possible. Remove the old pan by grinding the spotwelds. Slap the new pan in the hole and start welding. I would stitch weld every 6-8 inches apart to avoid warping. Stitches can be 1/2" to 3/4" long.