I think your assumptions about width may be correct Heinz.
There is one other option of course and that would be to use the older (narrower) axle, it won't be much difference because the eye can detect just a few mm. Once fitted, see how it looks. Then you have options of taking a slice off the rear wings, getting bespoke wires or just wider tyres on the rear, assuming adequate clearance on the inner wing panels.
