What was planned as an easy job became a longer story because it was not so easy to rivet the flap bracket to the main spar carry through.
I reamed the holes for the spar bracket to accept the 4.8 mm rivets:
Thereafter I needed to touch up the 2K epoxy primer at a few spots and let it cure.
To prevent removing more rivets I followed the idea of Des and used AN3-5A bolts:
Rivet the other brackets was easy.