I cant remember what year we (Im ex-Norton engine build and service workshop) switched from liners to plated barrels, it must have been around that time though. So if upon removal of the cylinder head, it becomes apparent that you have steel liners...check they haven't sunk (straight edge across the barrel face). If it has, the best long term solution would be a revised Nikasil plated barrel. To be fair, straight edge the barrel regardless for distortion.
The head retorque, imo, is to compensate for a failing in the design....thermal expansion differences between the centre two 12.9 (if I remember correctly) and the outer stainless steel studs I really cant see as being matched. With expansion being compensated for by the cylinder head material...this for me is confirmed by how the outer fixings appear to be sinking into the head material. Generally the outer nuts would move approximately 60° during the retorque at 500 miles, but with the centres not moving at all. I dont know if breakaway torque was calculated into that procedure, but I do remember the TSB stating that it was not necessary to back off prior to retorque....so it must have been considered to some degree. But then again, I'm just a grease monkey....I'd welcome further explanation eitherway.
