Thank you all.
Chris. For a man so knowledgeable on things two wheeled, I would have thought that you could do better than that.
The "B" and "S" both appear to be original stampings, taking into account the style of lettering and the equal look in ageing in and around the indents. Yes I know that "Steve" may have got his hands on a correct style stamp and then buggered around with acids, grit and alkalines to produce an original effect. I would prefer to think at this stage that they are original, or close to original stampings and that somebody might be able to shed some light on the setup. This bike is in Oz, so I also wonder if it had something to do with the export/import to one of the allies at the time?