The other thing we forget is how accents change with time - I remember my grandfather (who was Irish, and maybe more likely to pick up on local differences in accents) telling me how people in Crawcrook used to pronounce the village Chraa-chruk, with the 'chr' like the back-of-throat classic Jackie Charlton Ashington 'r'. Don't think they still pronounced it like that now, but to me it shows how what is now a SE Northumberland coalfield accent must've been more widespread in Northumberland, and Mr. Bewick probably sounded a lot more like someone from Ashington area does now.
So I'm sure you're right about swAn, and it's also true that there's a lot of similarity between Northumbrian and Scots in terms of the words used colloquially ('bairns' etc.) as well as some pronunciations (heed for head...), but we do tone it down for foreigners from places south of Sunderland. And anyone who wants to hear what Scots-Geordie fusion sounds like should visit Berwick-on-Tweed...