I'm moving on to examine the post Coroner Gunn people, starting with his eldest son James Gunn. (I know that's the anglicised version of his name but for convenience I will use it.) There is very little known about James but some mythic Gunn history attached to him fails again, there's a surprise...
To explain. It is accepted that James Gunn did not die with his father, the Coroner, at the battle of or near St Tayres. James had either moved to Killernan before or after his father's death.
But why would James move from the Castle the Gunns are mythically meant to own? It doesn't make sense; castles are big enough to hold generations of owners. You certainly wouldn't leave it if you were the oldest son and so would inherit the castle, and instead move to the rural backwater of Killernan. And there is absolutely no story anywhere attached to a Gunn castle being attacked by Keiths (or others) and forcing James to flee.
The only logical reason for James moving to Killernan is that the Castle attached to his Coroner father was nothing more than a tied (albeit grand) house attached to his father's job and so with the Coroner's death the Gunns certainly had to leave. James may have left the Castle before his father's death to establish a home of his own at Killernan
The idea of a mythic Gunn owned castle fails again...
Castle Sinclair Girnigoe
There is archaeological support for Castle Sinclair Girnigoe being built on a earlier castle; this earlier castle I suspect (no more) was the one used by Coroner Gunn.