Wow, a truly epic C2C, never heard it done before. Ive just done West Highland Way but yours a lot more of a challenge.
You talking about as much off road as possible or looking for a mix of MTB and tarmac to de-epic it a bit?
I guess Braemar, Linn of Dee, Glen feshie could be one part of it.
And Corriarick pass Laggan to Fort Augustus.
And Great Glen Way down to Fort William.
The gaps you’d need to fill in would be Aberdeen to Braemar. Glenfeshie to Laggan. Fort William to Ardnamurchan. Not sure about those.
Others might have different suggestions for ways to tackle it.