I have modified my spreaders to be swinging without changing the original fittings. (see attached photos)
All you need is 4 x 20mm x 6mm SS bolts with Nyloc nuts and a bit of care and patience.
I have had these on for the last three or four events and they seem robust enough so far and they have been out in decent breeze.
The central slot is the only real innovation over spreader mods done by other classes. This adds extra strength to the obviously weakened spreader in action by sharing the gybe impact load to two points.
If you do this mod you will notice that the geometry of the holes and slots is critical so as to both allow a good degree of swing whilst leaving enough strength in the materials.
Don't blame me if stuff breaks...I did it because I don't care if mine do
Is the old tub faster downwind now? Well in theory...yes