Thanks alfilado. As stated above I've reassembled the BB and put back into (limited) use in the condition shown. But I'm planning on laying the Moto up for a complete overhaul sometime this summer, so I'll have another go at it and follow your recommendations.
My engineering gut was telling me this isn't too serious, since there is no metal fatigue or galling; and I assume any corrosion that raised above the surface quickly spalled off and combined with the grease as the bearings rolled over.