There are a few good Montgomery photos in one of those Roy Bacon compendium books, "The A-Z of British Motorcycles from the 1930's, 1940's, 1950's".
Look on pages 154 and 272. The picture on page 272 is really good as it isn't the usual catalogue shot but shows it in use. The rider has just parked it and is going indoors. You can clearly see the huge cast aluminium silencer Montgomery fitted on the frame downtube. Page 154 is a standard catalogue shot.
The model you're asking about is the 'Terrier'. Montgomery made various models called the 'Terrier'.
Essentially they follow the standard British lightweight recipe of the day. Villiers power unit, Webb forks, British Hub Co wheels, etc,etc. About the only thing uniquely Montgomery is the frame, tank and the cast pong box.
Why do you need to talk to an owner?
Cheers,