Originally studs were used, same used for window trim. Pop rivets or screw in trim studs. If at all possible I would use the welded studs. The will not loosen over time and no chance of water intrusion.
As for the location can?t help with today, no access to the car. In my case after stripping the paint it was very evident where the studs were welded. One thing comes to mind is using an acid etch to help find the location. Similar to how welds are examined or filed off serial numbers are found.