I've only run 1 marathon, the FLM last month, but had a half-marathon ability base to start from.
No particular advice except to religiously follow the 'get you round' schedule and certainly don't miss any of the long runs off.
The Loch Ness is a tough one as I'm sure you know. Is there not a flatter on ea round the same time?
Anyway, you can do it but make sure you do the long runs. Good luck!