Yes it definitely looks like Mortlocks that was in Hay Street, Perth. I actually purchased a Triumph speed twin from them around 1967. This photo is before my time though. They later went on to become Suzuki agents when BSA went under.
Interesting that they were a Calthorpe dealer...I don't think there were that many even in the UK....I made some parts for my pals Ivory Calthorpe restoration which is now in the motorcycle museum and thought it was a well made bike...
Whenever I see these types of photos I often wonder how long it took to get all the bikes lined up so precisely!!....Ian