Well, finally got my 31s on ...
After much unsuccessful hunting on my part for a set of 4.25" backspacing rims, Wooders Garage came up with a set of Cragar Soft8s in a 15x7 ... which gives exactly 2 inches extra track over stock (legal max) and means I can run 31s with no fouling of the inner wheel wells and no need to change the steering stops. Tyres hang marginally outside stock flares. Still have to see how I go with the front disconnected, but for the moment, all smiles !!
(apart from the test drive where a loose track bar gave me my first ever Death Wobble experience)