I had some leftover 7075-T6 from a work project, so I fabricated the firewall doubler for the fuel line pass throughs. Since I'm passing through both a 3/8 line for outgoing fuel and a 1/4 line for the purge line return, this doubler is a bit taller than the plans show. I referenced some wrench clearance info on the net to decide how far to space the fittings from each other.

I laid out the location of the doubler on the firewall and taped the doubler in place.

Before drilling anything, I broke out the motor mount to ensure the motor mount wouldn't interfere with access to the fuel line locations. It didn't.

Here's the doubler temporarily taped in position on the firewall. Doesn't look like there will be any interference with the motor mount, although I may need to file one of the mounting lugs for the starter contactor. (...or is that the master contactor? shrug.)

Since the doubler needs to be riveted to a couple of existing rivet holes, I needed to fabricate a hole transfer tool.

Here it is in action. This 7075-T6 is really tough stuff. It drills much harder than 2024-T3.

Here's the completed plate clecoed to the firewall.

This is the inside view where the bulkhead elbows penetrate the firewall. When I install these for real, I'll use the steel fittings rather than the aluminum ones shown here.

Last thing for the day was to countersink the rivet holes in the doubler. I'll anodize this before installing it.