Thanks for the additional tips. My plan is working out similar to your suggestion. However, the car hire prices seem very high. Two days, pickup in Glasgow, return in Carlisle, is 93 pounds. Last year, I did five day, pickup in Dundee and return in Glasgow for 150 pounds; and I overpaid, as I remember it. Both rentals were through Hertz for a small car.

I'm guessing the public transport in the western islands will be like that in the Borders; just barely possible to make it happen if timing is perfect. That hunch won't stop me from spending a day this week staring at time tables to prove that.