I've fitted my new wheels and 205 tyres to the back of my morgan, and it appears that the drivers side tyre sticks out about 5mm more than the passenger side.
Is there any lateral adjustment in the rear axle - it would only require a 2-3mm shift to the left to equalise it.
Would a panhard rod do it? Or do I need to fix first and then use a panhard to keep it in place?