a picture paints a thousand words. This ain't mine, it's a spitfire, but it's the same rear set-up and shows the camber of the wheels with no weight on the body. It;s quite a lot worse that this on a herald. Although looking at that pic has made me wonder how wide a spitfire spring is.
1/ new rear spring (or strike it lucky and find one that has the correct distance between eye's- about 40 inch's with very little "arch" in my case)
2/ fit coilovers. this option means I would need some way of "tieing" the upper spring mounts to the top of the diff. to prevent them from rotating
3/ fit a complete replacement rear axle (and potentially lose some points towards my re-bodying plan)