Looking back, I found what Malcolm Douglas had to say about how Dick G arrived at the tune variant he uses:

On revisiting it, the tune Dick Gaughan uses is much further removed from Foodrage than I'd remembered. Gaughan himself (I think this was mentioned in one of the other threads on this song) didn't recall where he got the tune: it sounds to me rather as if he started out with the tune in Child and subsequently mixed it up with bits of Foodrage.

Child's example was from William MacMath, learned from his aunt, Jane Webster, September 13 1886; she had learned it some 50 years previously from a Samuel Galloway in Kirkcudbrightshire. That was the tune that Andy Irvine had intended to use, though of course it didn't belong with his text, which was mostly Child's example A, anglicised and with some alterations and borrowings from other versions. The hero's name in the MacMath MS was John Barborough; in most English and Irish forms of the song he is John or Tom Barber.

The only performer I have ever heard doing Foodrage (Child 89) to the 'right' tune is Brian Peters. It's in mixolydian mode but is often squashed into the minor (by those doing Willie o' Winsbury) which sounds a bit off.