Looking at the rake of the funnel, I'm sure it is "SCOTTISH STAR". The other reason for believing so is that she was sold to the same company as "PORT INVERCARGILL" (Deferton Corp. of Piraus), and renamed "KAVO YERAKAS". She was laid up from 1975, a year after the date of this photo, until 1979 when she was broken up at Bilbao.

Could the vessel alongside be the Scottish Star which was also trapped in the Suez Canal?

Port Invercargill doesn't exist as a geographical entity. The city of Invercargill is 30km by road up the New (or Oreti) River estuary from the Port of Bluff. I presume PORT BLUFF wouldn't have fitted well as a name for the company at the time.