Dirk,

To answer your original question, you can not sucessfully adjust the spreader arms that you have. I too have a set of these arms & they only fit in one position ( I guess if you re-fair the end fitting, you could reposition the spreader & hence the rake). The only adjustment from there is the position of the wire at the tip of the arm ( up to 20mm max).

The only way to achieve more adjustment is with a proctor style arms.

Marcus