I'm sorry but I feel the conjecture here is getting way out of hand in more than one way. It is extremely unlikely that any of these pieces predate 1690 or come anywhere near it. Richie, please present what evidence you have for this theory and then we can discuss it.

Buchan probably read about some incident in a newspaper and decided a few of the facts fitted in with the version of BA he was concocting.
Scarling town surely just derives from 'Scarlet town'!

By all means look for a Captain Green but don't bank on the suicide part.

Let's remember we are dealing with a man who manufactured ballads from bits and pieces from here there and everywhere. Like Scott he tried to include real people's names contemporary to his time and members of families who were likely to buy his books. (In this case it was never published mainly because by then (1830s) his contemporaries and publishers had got wise to him.)