Welding

You should always put the ground close to the work. Not just in this instance. On these old cars just disconnecting the battery is really all you need to do. If you have a newer MSD that plugs in or other brand with a plug, it sure wont hurt to take the extra precaution. If its got fuel injection I would disconnect the module.
Cover your nice paint around the area before welding to keep spatter off it. They actually make a masking paper specifically for this.