This is not a straightforward question.
As Forfarian points out, a number of paths on old plans, in effect shepherds' trails, have long since disappeared.
My grandfather was born in 1875, eight years before Lawson's Tarmac road north from Lairg was laid down. His understanding was that before the road was built along the east bank of the Dionard, the traditional route to Durness traversed the valley between Loch Caladail and Loch Meadaidh (both then smaller as they hadn't been dammed) and met the main village at the top of Sangomore.
The road was considerably higher than the modern one, possibly closer to the summer sheilings, and is traversed by a number of mountain passes leading from the Kyle of Durness to Loch Eriboll, that would allow the drovers from Loch Hope and the West Moine to meet the path south.
The route from Allt Ach a'Chorrain does cut through some of the lower ground north of Cranstackie and south of Meall Meadhonach and would have met the old north-south path about a mile east of the present road. There were several small townships to the east, who would need access to the road south
I haven't walked it, but it looks a lot easier than the Bealach further north between Meall and Beinn Ceannabeinne which is easy on the west but not on the east.
