Thank you Bart and to others who sent me emails with details. Charlie has agreed to either do the ferrying or to find me someone who will, he couldn't have been more helpful.
Simon

Good to hear you have made some sort of arrangement!
Obviously Charlie is still residing in Achnanellan. It's a beautiful isolated spot.
When Charlie ferried me over in 2011 he did not have enough petrol to bring me all the way to Polloch (quite some extra miles), so instead we went just to his house in Achnanellan and he showed me the way through the woods to Polloch. That route is not on the map, but there are clear forest tracks.