Very nice tune, where have you learnt it from?
I personally prefer to play it in pure A mixolydian, G natural in the bars 1 and 5 of the second part.
The Maid of Glengarrysdale
This tune is actually called "The Maid of Glengarrysdale", and it’s likely that dafydd got the tune from The Battlefield Band’s At the Front LP (from Antwerp library?).
Very similar to "Roman Wall"