The thickness of the plates of the upper triangle is also non-uniform.

Belt sander and plastic cards plates then come to the rescue ...

After bonding, they are reinforced with U-shaped aluminum profiles, and new slots are made in the ribs

After many dry tests to properly align the assembly (sanding, adding plastic card and the ribs) the two plates are bonded together: first, few drops of cyano for adjustment, then Pattex 100
% They are then just screwed on the model, not yet stuck, so I could get them off to light the model later.

The back shows a serious gap, filled with a resin bit.

Front, the raised plates are shifted between right and left sides. they will be adjusted later.