This is one of the two stiffeners adjacent to the firewall recess. You can see how the flange bows outward (aft) from the joggle. This flange, however will interfere with the aluminum panels which will be mounted to the aft side of the firewall, so I'm going to have to file this bulge down.

Here's the other stiffener after filing.

I drilled the floor and firewall panels for #8 screws and drilled for nutplates on the flange of the floor panel. In the past, I've drilled the center hole large enough for the screw, threaded in a stubby screw, and used the nutplate as a drill guide for the rivet holes. Recently, however, I heard about a technique to make this somewhat faster...just drill #30 and cleco the nutplate in position while drilling for the rivets. After the rivets are drilled, enlarge the #30 hole up to #19 for the screw. It seemed to work great. I also dimpled all the nutplates necessary for the left and right hand sides.