The brackets of the right tank didn’t lean on the main spar for the top holes, this needed some shims to fill the gap. This gap is a result of the other issues I had with the main spar.
Between the main spar and bracket 1 is a space of about 2.6 mm:
I created some shims from T2024-T4 aluminium.
Due to the thickness of the spacers the bolts of bracket 1 and 2 of the top holes are too short. I ordered some longer bolts from ACS.