I riveted the top rail to the skin mounting angle. This was a difficult task once the rail has been riveted to the firewall, but at least I know it will be riveted together correctly. I used washers to plug the original (wrong) rivet holes as they have been drilled out more than once. The new rivets are next to them.
Since I used stainless washers to provide a grip hole for the plug rivets, I sprayed primer over them to prevent or curtail any galvanic corrosion in the future.
