thanks for showing the spot-weld procedure Dave! Is every spot-weld seam leaded, regardless of manufacturer (would my 69 GTO require similar procedure)?
The lead thing used to be reserved for open panel seams.
More of a common knowledge "lead seam" is the sail panel where the top of the quarter meets the roof cap. It's a lead solder seam, the sail panel is the best known but they used lead where the rockers meet the quarter and also where the A-pillars reached down to the cowl on many cars from that erra.
I melt it out if I can (if it needs to come apart) instead of grinding, lead dust in your lungs is probably bad.
69 GTO would be put together much the same, but no you wouldn't have to cook the lead out unless you had to do a repair to that area.
When I put these areas back together I typically don't lead solder them back together, they get welded and then I use a filler called "metal to metal" which is basically aluminum dust with resins & hardners, it mixes up with a liquid hardner and I'ts kind of a modern replacement for lead.
