Hmm...
Regarding body disposal.
There are many places where a body could be left, and it would not be found again, and require no tools.
Examples include: disused wells, mine shafts, pits (that are full of water), tanks that are used for disposal of cow manure, pig manure, etc.
Given the size of the area you are discussing, I'd guess there are hundreds of places like that out there.
The only way that would come to light, would be if the person that disposed of a body, talked about it.
Yeah, here's the only mine working in the area. There's absolutely no chance of getting near it from the A85. The railway line cuts it off completely, there's no access road, it's on a slope of about 20%, and it's forested on the lower slopes.
This is what he was up against. He was driving an ordinary saloon car, and he could not afford to take that car anywhere it might get stuck or he was toast. As it was, he seems to have damaged the suspension. But he could only take that car on made roads or reasonably passable forest tracks. My own thought was that he was unlikely to have been able to get the body more than about 100 yards from wherever he'd stopped the car, but maybe we should consider 200 yards to be on the safe side. Then when I spoke to Stuart Houston he said exactly the same thing. They
never move the body more than 100 yards but we searched 200 yards from the roads just in case. (Louise Tiffney was found EIGHT METRES from the side of a busy public road, fifteen years after she disappeared.)
We're working on the assumption that the disposal place is near a road or track accessible from the triangle made by the A85, the A82 and the B8074, plus the A85 west to Dalmally. We've examined every turning off these main roads, and it's surprising how very few are actually practical given the time of day, traffic, gates and the terrain. There are really only three serious possibilities, of which the stand-out leader is the track up the side of the Allt Broighleachan.
There is another wrinkle, which is that we're pretty damn certain he knew where he was going. That he was going somewhere he had been before. (The cops also think that, as regards the R&BT, which makes their theory that he drove around for hours in a panic of indecision even more surprising.) As Alduma pointed out earlier, that changes the parameters a bit. It doesn't matter if the Allt Broighleachan picnic place is the best place in Scotland to conceal a corpse, if the place he had actually been to was one of the other possibilities. But having said that, the Allt Broighleachan is also the most likely place for him to have visited. Although it's not at all busy, in fact it's very quiet, there is a picnic place, a somewhat interesting patch of ancient forest, a mountain bike trail and access for climbers up to Beinn Mhic Mhonaidh. There was a sign by the bridge welcoming visitors. (At first I discounted it because I thought that meant it would be too much frequented, until I realised how quiet it actually is, especially on a weekday.) It's almost perfect. Quiet enough to be unobserved, but open to the public so that the "what on earth is that car doing there?" question wouldn't arise the way it would anywhere else.
If he had been there before that is. But he went somewhere, and nowhere else is nearly as promising as that.