Ah. The clue was in the cross section drawing of the bolt they provided, showing a thin metal cap. Chisel be damned though - be a bugger of a job. Out with the angle grinder to take most of the cap off each bolt, then put triple clamp back on the steering head bolt and with a drift, tap the switch body off. Phew. Wish they gave us Aussies just normal bolts...... Now have to extricate the old bolts, then open up the switch body and do the cleaning and shaving of the wafers.