i believe the camber all works together with the toe in and out but quite right in saying there shouldn't be a difference in camber if they're both set the same on the toe which they are can you be more specific about the wishbone bushes! as the only ones i know are the tie rod ends sway bar and the donuts!
The inner bushes on the wishbones have a void in them on the horizontal plane to allow the tie rod to pull the wishbone slightly, it`s this action that gives them the passive rear wheel steering
If you look at this picture you can see the inner part is hollow compared to a solid rubber bush

Without looking at it side on you can`t see the where the hollow bits are but if you ever have to fit some they are extremely rather tight and have to be fitted in the correct orientation, the solid bits top and bottom and the voids left and right.
The outer bush on the wishbone is just a normal solid rubber bush.
@ mrgreen, just realised you`ve got a Desmond so your rear suspension might be slightly different. The 3.0l Carltons had the same set up but the smaller models didn`t have the void bushes or tie rods and I don`t know if the same applies to the Omegas. If your car has rear tie rods then it will have the void bushes too.