Thanks to Noodley, I've been able to plot the route into Bikely:
http://www.bikely.com/maps/bike-path/144415
HTH
Ah, I see you go through Sanquhar.
I once did Mr Applebag's 300 perm that goes through Sanquhar twice, on the way out to the south west, then on the way back to Lanark.
I controlled at the filling station on the way out, and it seemed to make sense to use the same place on the return.
It was the same lady who attended to me on my second visit.
Filling Station Lady: "So where've ye been son?"
Me: "Oh, over to Maybole then down to Newton Stewart."
FSL, calling through to the back shop: "Haw Wullie, come here an' see this: there's a boy here an' he's been a' the wey tae Newton Stewart an' back again the day - on a f*ing push-bike."