After cutting a strip of .025 thick material to act as a spacer across the entire width of the fuselage, I got to work getting it drilled to the sub panel flanges.

Drilled and clecoed in place.

I've never drilled the flanges of the firewall that rivet to the upper top skin, so I used Van's prepunched skin as a template to drill those flanges. It's not really necessary to have these holes match Van's, but I might as well. Even with a new drill bit, some of the holes drifted, elongating the prepunched holes in this leftover skin. The resulting holes in the firewall flanges looked good.

Clecoing as I go. However, now that the relatively flat center portion is done, this skin needs to follow the curve of the firewall.

That was going to be a major pain to make this .032 thick skin follow the curve, so instead of that, I just hacked off the row of holes.

This 5/8" wide strip is easy to wrap around the curvature of the firewall. Also, this photo highlights how some of the holes in the aluminum were elongated while match drilling. No matter.

All drilled and deburred.

Now to clamp the new skin on and drill to match the firewall. I only drilled three holes in proximity to the center rib and the left and right pairs of ribs. Why? Because the firewall is such a flimsy piece of sheet metal that if I were to just drill all the holes through the fireall flanges into the skin, the present waviness of the firewall would be locked in for all eternity. Instead, I'll use that strip from Van's old skin again...

...to drill a few additionall holes in my skin, roughly between the center rib and the left and right outboard ribs. It may look like this drill operation is going to drill into the firewall, but I actually have the skin propped up on a thin strip of wood, not visible here. The clecoes only go through the strip cut from Van's skin and my skin.

Okay, the center, flat-ish section is drilled. In order to make my life much easier, I'll need to curl the skin outboard of the ribs before match drilling those areas to the firewall flanges.