Way back what seems like 100 years ago, this is what the firewall looked like. Specifically, the flanges holding the cowling on the airframe were in pretty bad shape. Not exactly something you'd [I'd] be proud of.

I removed the big ugly flanges and was left with the original stainless steel firewall.

Unfortunately, the original firewall flange looked like Swiss cheese. I didn't cherish the thought of trying to work with pre-existing holes. Additionally, the original installation had the sheet metal covering the gas tank attached to the firewall and then the fiberglass cowling going over the top of the sheet metal and secured using machine screws and HUGE tinnerman washers. Again, not exactly something I could be proud of.

I started off by fabricating new flanges to be attached to the lower part of the firewall. I made mine out of 2024T3 .063" thick. Comparing the original (on the left in this picture) to my new flange, I think I like mine 'mo better.

And here's mine clecoed in place. I decided there was no good reason to have a flange taking up space where the cowl cheeks would be installed. That's why my new flange doesn't go any higher along the side of the fuselage.

Two things to take note of in this picture are: (1) I installed a small additional flange fabricated from .063" material; and (2) I cut the top part of the original flange off the stainless firewall. I just decided there wasn't enough good material remaining to even work with.