Body sheet metal vs floor pan

Just picked up a Dart Sport to build into a bracket car - it's super straight, except the floor pans, which are totally rusted out, and the trunk pan, which I'd prefer to patch up. I still have most of the car this one is replacing, my poor (crashed by an idiot) 73 Duster. Meaning I have a ton of sheet metal at my disposal. Can I use any of its body to cut out patch panels? The old hood is bent up and useless as a hood but would provide a lot of clean metal.

Are the body panels a different gauge than the floor pans or trunk pan?