The cowl hinges were just a touch too short when manufactured by the book. It called out for 25.5” length, but that left a solitary rivet hole on the upper firewall that didn’t connect anything. I re-did the long hinge at 26” and the last half inch fit under the previously empty rivet hole very nicely. You’ll see a close up of that area on the 2nd photo.
Upper Firewall Assembly (upside down)
Firewall Fuselage Doubler, w/ Nutplates & Hinges
I tend to be the kind of guy who makes several forward steps and then a good backwards step to keep away from being too efficient. I drilled out all 25 nut plates in order to dimple the firewall fuselage doubler and then re-riveted the nut plates. In the photo above, the piano hinge that is to the right of the vertically oriented nut plate is the one that is 26” vice the 25.5” called out by the book. You can see the rivet that would otherwise be pointless helping to secure the piano hinge.