The Strontian- Polach trail up past the old lead mines rides much better S to N, as the descent on the Shiel side of the hill is much more fun than the cattle-damaged Sytrontian side. It’ll be wet this autumn mind.
I’d def stick to the two mentioned above- the Shiel side track works fine for a gravel bike as an out and back or part of a much bigger loop starting at Glenfinnan, back to Loch Eil, around to Ardgour & Strontian and over the hill to Pollach/Shiel. This is mostly very quiet singletrack roads and that way aroud keeps the gravel for the last third. On a good day, stunning views the whole way around.
Morar out and back is a classic trail ride.