Brilliant, I'll post some photos later.
Corrour Station/Loch Ossian was stunning, the roads were frozen solid and there was some ice about, but nothing that slowed us down. Once we left Loch Ossian behind the track got a little wetter from thaw, then turned back to mushy/slidy stuff on our way into the Loch Laggan forest.
I feel we may have missed an opportunity with the tramline, because the farm tracks we rode after the Monessa gorge bridge would normally be very deep churned mudded, but they were frozen solid. Makes me wonder how the tramline would have ridden after all.
Once we got into Leanachan we mostly followed the puggy line straight through, although some of it had been obliterated by forest roads and there was a 100metre section that had some fallen trees and unrideable forester tracks on it. We ended up getting a bit lost and found ourselves on the flat 'middle' section of the DH track (after the steep stuff, before the motorway) which we had no choice but to ride. I loved every moment of that but my mate was less sure. After that it was puggy line all the way (in the dark by this point) into Ft William. I feel I missed out on this bit, I'd forgotten my headlights so was riding a bit blind but my impression was fast, easy singletrack on a slight gradient all the way to the aluminium works. We met a couple of guys out on a night ride halfway down who pointed us in the right direction.
We then rolled in to Glen Nevis hostel watching a string of headtorches coming down off Ben Nevis in the dark, all the way from the summit, which was pretty epic.
Next day was a fairly standard route from Ft William to Glen Coe on the road, through Glen Coe on the little track (thanks Bullroar, although you forgot to warn us about the massive, rotten deer carcass down there! ) across the top on the old road again (stopping to investigate 'The Squirrel's Drey') then onto the WHW to Tyndrum (skipping the techy bits where possible, we were on ss CX bikes).
Great ride that I'd do again for sure, once I figure out how to stop my knees hurting so much! Would recommend the route although it would probably be a bit dull on mountainbikes.