I continued riveting the stiffeners to the firewall. The firewall has steel powedercoated brackets located at the 4 corners. There was some powder coat buildup on the holes, which I had to ream out. To protect the brackets against corrosion, I decided to apply touch-up paint to each rivet before installing them in the holes.
I had a tough time back riveting the rivets around the brackets. After riveting, the manufactured head of the rivet would sit proud. In the end, I just decided to buck these parts. 