To make it as strong as possible the extra piece was hammered to a "hat shape" so it attaches under the fender's edge on both side. The outer side of the rear fender had to be shorten to keep the original shape and to line up with the running board.
Btw the +5 cm should be over on the limit where stock running boards can be used, at least mine looked awful (no pictures). The front section of the fender was sliced up again and got a "V" shape so the bottom edge is near to stock now and it looks ok to me.
After the second test fit it was good enough to go ahead, time to extend the bumper brackets (30mm) to clear the fenders.
This is it for now, I hope I get them back from the painter in a few days/weeks.
I will have to relocate the rear lights once the fenders are ready