The top of the lower firewall needs to be flush with the top of the stringer so I filed the lower firewall holes for a better fit with the stringers and longerons.
The firewall is positioned in exactly the right place but there are some foam gaps between the fuselage sides and the firewall so I sanded some shims to fill the gaps.
This was about 4 hours of filing and sanding and trial and error fitting but I’m pleased with the result.
