So if you hadn't guessed I am going to have a fun time trying to get the wheels to fit under the standard arches! But with help from willtheyfit.com and a bit of maths I have worked out that the rim itself will stick out a further 8mm. For the old wheels to fit all that was needed was the lip rolling flat so I think I should be able to roll and flare the arches enough to get the new ones under with slightly smaller tyres, which are currently 295s.
Has anyone had any experience of fitting 11s on the back of an s14?