I have been wracking my brain to come up with a place local to the Mauchline area that would equate with the "Scarlingtown" given.
Roughly six miles away, a mere hop step and jump to folk who thought nothing of walking fifty miles in a day, we have the Clachan/Estate of Skerrington. Near enough in distance and sound to qualify as a contender.

Verse 34 as given could be compared to the last verse of a ballad collected in Dumfrieshire by Burns :---

For it"s I hae castles and I hae toors
I hae barns and I hae boors
And aa that is mine it shall be thine
For the rownin it in thy apron.

The full ballad can be found as no. 3 on the disc MTDL613 entitled there as "Oor Young Lady".

I am not sure that this ballad appeared in print in the lifetime of Buchan. [O.Y.L.]