The man standing in the doorway was identified on the back as W Keating.  On the same embarkation roll page for Gordon Williams was a Walter Birmingham Keating, a 19 year old clerk from East St Kilda

In a different album, but also featuring the 6th Field Ambulance is another photo which shows "Wally" standing on the left at the side of the Ajana on her departure from Port Melbourne in 1915.  The identity of "Scottie" is difficult to discover, but I wonder if he is the corporal on the left in the photo below, which has Harold Williams on the far right?  The photo below is during the period that Harold served with the 12th Field Ambulance, during 1917.