In reply to Tim Davies:
The track's good, though I've only cycled in as far as Beinn a'Chaisteil from the South.
I parked by Black Bridge, and had no access problems, but this was in 2008.
This may not be of interest, but you can get closer from the North, up Strath Mulzie. And it -used- to be possible to drive to Corriemulzie Lodge, where there's a "walker's car park"; I haven't been in recently.