I have a Magnaflux test kit, I have used it once and got inconclusive results, that is why I changed the arms. I thought that as the arms were the likely culprit I would swap them out.
I will indeed clean off the paint on the old arms and test them. I have visually inspected them and they look fine. I spent time looking again today and if the forward pointing section of the bell crank arm nods inward, and the steering is held tight then the top of the swivel pillar would move inward pivoting around the forward joint on the steering side arm. This would produce the symptoms I have of the rear of the road wheel going inward, and the front edge turning out.
The brace I fitted is therefore going to be under tension, and the forces will be pulling directly down the centre, in which case I think the design will be strong enough.