I understand now, you want to walk northwards up the coast to the castle.

As Cplin says, apart from the short section just south of the castle you are talking about a bit of an assault course. Excellent views and interesting places such as Fowlsheugh and a cracking pub at Catterline but there is no official path. You can normally stick to the field boundary but you may find yourself plodding through a freshly ploughed field or neck high oilseed rape.
There is a good coastal path south of Inverbervie to Tangleha' at the northern end of St Cyrus beach but, apart from the first 1/2 km, north of Bervie it is "Who dares wins".

Thanks everyone for your responses.
I'd looked at the aerial imagery and thought I could see a path, but your comments and expectation setting are most welcome. The closed cell mat has been used similarly in the past .. normally when you can't clearly discern which side of the hedge/fence that OS green dashed line runs only to find it clearly wasn't the side you picked and the field style sits enticingly in the adjacent field while you're faced with a challenging fence to negotiate.

Colin, I was drawn to Clachnaben after your suggestion and description of the landscape of the approach. Fingers crossed for decent weather to appreciate it at its best.

Andy

While I consider myself one to step out in style (I wish) , you'd have a job scaling a fence in style , much easier with a stile!

Andy,

If going from Tarfside, I’d recommend heading north on the track up the Water of Tarf (?), then east to walk the whole ‘ridge’ from Craig Soales, over Mount Battock and ending at Clachnaban with your first view of the coast. What a memorable day on my first challenge before tackling the Fetteresso and onto Dunnottar Castle for my finish. I took a bus to Montrose on the main road just south of the castle.

It doesn't sound ideal, but in fact you've picked a good area.
https://www.geograph.org.uk/browse.php?p=706831
https://www.geograph.org.uk/browse.php?p=707731

Thought I'd post this for others that may come after.
As Colin says the coastal path north from Crawton soon becomes absent and you're in the field margin. The local farmers aren't on any 'field margin' compensation payment so they are non existent , and I can only admire the skill involved to drill so close the field boundary. None the less a way is possible without destroying precious oats/barley, but not one to do in shorts. Since you stick close to the actual cliff top your distance estimates will be off a fair bit.