I did a LOT of laning in Scotland up till about 10 years ago, when other things got in the way.
During this time I researched and drove lanes in and around Falkirk, Stirling - many in Fife, the Borders and the Lothians and of course did the Corrieyairack a few times. Last time I did it was probably around 1997 and from the photos it looks a lot worse now than it was then - which is a real shame. When we did it one of our drivers was in a hand controls rangie - it was tight but we made it through and I have some photos of it all somewhere....
On the way back we did a few other routes along the side of the lochs in the great glen etc. and then cut back across tot he east and had a go at the minigaig - never have managed to complete it however and would not recommend it nowadays wihtout a full pre trip planning session.
I did have a load of maps which I marked up lying around and a lot of my research material into the legal status - the primary aspect of which is desuetude, it being incumbent on any person defining a road to have lapsed to demonstrate that it has not been used for a proscribed period.
i have no idea where they are, but if i can find them and anyone then wants to come and pick them up from me then I'm happy to pass them on to anyone willing to pick up the threads from there.
I've also got a copy of an article I did for LRW at the time which explained the situation and processes of defining whether a road could be legally driven in a bit more detail than I can do here - the definition of private roads is particularly complex, since a road can be private (with regard to the ownership of the solum, but a right to traverse it can still exist for the public - which is in fact the status of the corrie).
Re the sections of the West Highland Way. Yes they are driveable in terms of condition and physical access, however I would not recommend doing so. As part of a long distance path network they are subject to special legislation and are VERY heavily used by walkers. They should (IMHO) therefore be considered out of bounds to laning use unless you are very brave or just don't care about rubbing people up the wrong way.
You might be safer doing the minchmoor route in east lothian - a nice drive, even in early winter, though it is entirely possible that its adoption as a leisure cycling route may have led to the creation of bike stiles and fences along the route - certainly many of my local (and much loved) lanes have been fenced in by local councils over the past five or so years as they turn them into local walks - possibly illegally, but that is a battle someone would need to go out and fight.
O.