I have been looking at West Highland Line and Kyle of Lochalsh / Thurso line trains in the Andrew Vines 'Diesels in the Highlands', Michael Palin's Great Railway Journey in 1980, videos on YouTube, and other pictures on the internet. I have been trying to work out formations. An obvious difference between Mk1 SO's and SK's is that the SO has only a few roof ventilators, whilst the SK has many. The brakes I try and recognise from the coach side patterns - the number of seating area windows and pattern of brake area doors and windows, also noting that the BSO's may be BSOT's (Buffet label in end window and short red line above the window). I have also noticed Mk2z or Mk2a coaches in use also.
The train at the end of the Michael Palin film I believe is Mk1 SO/TSO and Mk1 BFK hauled by a class 27. WHL trains in the 1980's were mainly formed of 3-4 coaches, though there would be more coaches in the high season. The tank wagons (TTA not OTA which are the timber wagons) were only used in mixed trains between Fort William (fuel depot) and Mallaig for the fishing boats. How the tanks were shunted onto the train I do not know.