I now have a line drawing sent by Roy of the 1948 model which shows a low mounted light switch with ammeter directly above. I cannot see enough detail in the Youtube pictures but I do have a picture in Jeff Clews book of his 1947 model (girder forks unlike my Oleomatics) but which appears to have a similar layout. Thus, it seems I need a Lucas ‘panel’ style headlamp like one of these;
