evilstepdad:
May I suggest a pneumatic seaming tool. I have used mine extensively in replacing the floor pans, inner rocker panels and kick panels on my '66 K-10. I will also be using it to replace the rear half of the fleetside bed panels on my '66 C-10. It is a great tool that creates a 1/2" offset in sheetmetal to back up the piece you are attaching. Avoids the blowout you get if the metal is a little thin for the power setting and/or wire speed of your wire feed welder. Speaking of wire feed welders, I suggest investing in one if you plan to do any extensive amount of panel replacement on your '60. I bought a Miller 175 that runs .030 wire and shielding gas. I think a monkey could weld with one of these machines with a little coaching and a few bananas. Good luck with your '60.