I got my bonnet back. It was welded and now, I have quite nice louvres.
In the past the skin of the bonnet must have been removed. The old rivets were still in the tube and made a noise like a rainstick/rainmaker. I drilled a 8 mm hole into the tube and got this:
Then I tried to close the hole.
Fired by the success to close the hole and not to have widened it I thought it is time to modify the right exhaust header. First, I tried it with an old tube.
So, I made some cuts into the exhaust headers
bent it with an old jack
and welded it together
The quality of my weldseams depends heavily whether I find a comfortable seat position wrt. the object of welding. Nevertheless, after sanding everything was fine (and closed!!!).
And it gave the the desired space: