Gravel / Gravé / Gnarmac / Groad / ATB

Actually, it looks like there's a track heading north from a farm just off the a811 that eventually joins that road to Dalmary etc.
You need to be too zoomed in to see it to post the whole thing in one screenshot but you get the idea.

Ha! I've been on openstreetmap and google maps for the past hour looking at the very point you highlighted. I'm gonna go back out later in the week to check out how that path is.
I'm starting to think that Old Drymen road up towards Dalmary might just be the best option. I'll call it a Groad ride so I can say its 100%