Riveted the firewall stiffeners and corner hardware in place. No issues. Had to use one pull rivet in a nut plate that there was just no way.

Thought I was all done and started researching potential firewall insulation. I saw a picture of some else's firewall and noted the had riveted the recess to the wrong side. Then saw another photo where someone else had done the same. Checked the plans - turns out I'm the one that did it wrong. Wasn't too bad to drill out those rivets and fix.