Thank you for posting the feedback. This information is invaluable to us and sometimes it is quite hard to get it from sailors...
I should mention however that there is a mid-way position, you just need to keep the tiller up. See the attached photo. It will take some tries in the water to understand the principle.


Also, we've never received reports from South Africans sailors about excessive weather helm with
the rudder 20-2. I think all the problems could be solved.
Lets look on the problem from other side. Pressure on the tiller is the result of center of efforts(main-sail and jib geometric centre) is being too much distanced from centre of lateral plane. In order to solve this problem there are two hints:
1. Maybe it will be possible to rake the mast more forward?
2. Maybe it is necessary to increase the pressure on the jib and remove pressure from the main-sail.

Usually this helps. I'll try to follow up with Graeme, in hopes that his old email address is still working.

About the rudder box and blade weights and dimensions you can refer to this page: Rudder box 20 series - Blade 2

Happy sailing!