Here's the new flange drilled and clecoed to the firewall. That's a lot of clecoes!

You can see how I have the flange sitting above the firewall by approximately 10mm. This was partially a WAG and partially a measurement based on test-fitting the cowling.

Sorry for the out-of-focus picture, but you can see where I guessed pretty close on the height of the flange. The cowling is just sitting naturally on top the new flange. At this point, I hadn't even bent the flange to match the 99 degree approach angle of the fiberglass cowling.

After doing a little math and drawing a few lines to determine the edge of the flange and where I wanted the holes to line up, I drilled and clecoed the top of the cowling to the new firewall flange.

I spaced things such that I'll be able to use this flange to attach the piece of metal that covers the gas tank, too. I'll just use K1000 nutplates to attach the metal. The fiberglass cowling is going to be attached using Camlok 1/4-turn fasteners.

I couldn't help myself. I had to tape the cowl cheeks in place to see how this whole thing is going to turn out! The cowling is clecoed in place with all the holes drilled. The cowl cheeks are going to need major fiberglass surgery to make them fit. Bummer. Do-able, I guess, but still a bummer.

I'll try to remember to add a better close-up picture below, but this was the initial stage of fitting the cowling. If you click on the thumbnail to the right and then zoom in on the back of the spinner backplate, you'll notice a particle board spacer. I fabricated a ring of particle board and attached it to the back of the backplate. The 3/4" thickness of the particle board along with the depth of the flange in the backplate worked out to provide me a very nice, consistent distance between the forward edge of my cowling and the back edge of the spinner backplate.

A friend of mine with a Sidewinder teased me asking if I really wanted a gap that large, but I'm comfortable with it. I guess I'd rather give up a nano-knot due to loose spacing rather than having my cowling chewed up because my backplate rubs!

I guess this is a slightly better shot of my particle board spacers. The first spacer is behind the spinner backplate. The second spacer fits over the propeller studs so I can bolt the backplate onto the crank without the thickness of the propeller itself.

I actually drilled and clecoed the cowling to the particle board backplate spacer. I think I used 4 clecoes in each half of the cowling. This kept the cowling securely up against the spacer as I was fitting and drilling the firewall side of the cowl to the flanges. I cut the square out of the air intake snoot to allow me access to the inside of the cowling with a drill and clecoe pliers. It still looked like a bit of a circus act trying to reach up inside...

I wanted metal flanges holding the cowling halves together so I fabricated this flange from some .063" stock. Probably overkill, but I'd like it to be sturdy.