To get a better understanding of how the other parts fit together I did a test fit of the firewall and the top rails.
The aileron AP bracket is a bit too high to fit between the main spar and the ribs, it seems that the height of the bracket is not corrected for the thickness of the collars of the rivnuts:
It’s quite obvious how the parts of the firewall fit together but the parts of the top rails are like a puzzle. Some holes need up-sizing to 4.1 mm and some holes don’t align 100% through the stacking of multiple layers. But overall the fit is quite good and I’m happy with the progress:
Gusset view from the outside and inside: