After some cutting back on the rear line, I'm getting so close to the edge that it becomes important to be very precise. My issue at this point is that the horizontal sides are still too long on the top cowling and overlap the bottom cowl. This squeezes and deforms the bottom cowl a bit causing some shift in shape which makes me wonder if the line I'm making on the firewall will remain accurate once the sides will be cut. So I made the decision that I will start cutting the horizontal sides close to where they need to be and then re-evaluate the back at the firewall.

In order to do so, I decided on the final height of the bottom cowling horizontal line and sanded it flat. Next step was to draw a line where the rivets would come for the flanges attached to the bottom cowl horizontal line. I used a flexible tape measure to draw a line.

Then verified it with the laser level. As you can notice, mu bottom cowl side line is not perfectly level with the airplane but it's not noticable so I kept it as is.

Clamped 2 flangs on the horizontal sides and exposed the tabs by 0.20". With these 2 in place, I used the steel rules to extend the centerlines on the side of the fuselage skin. This defines the center of the FSF-L flange receptacle. With that defined, I drilled the FSF-L in place. Next step will be aligning the rest of the flanges on the horizontal line and drill them to the bottom cowl.