First, there is no known "original" of Willy o' Winsbury -- Child has nine texts! Bronson has 22 different tunes for "Willy."

For that matter, Bronson has three different tunes for "Fause Foodrage."

My guess is that the tune you're referring to is the tune sung by Pentangle (at least, that's the attributed source of the people I heard it from). That seems to be far the most common tune today. But I've heard what I would consider to be three different tunes. And Bronson lists four tune-groups. By far the largest group (15 of the 22 tunes) is what he calls Group D. This is known primarily from Sharp and/or Karpeles and is almost entirely North American (Hammond had a "D" tune from Dorset).

Group "C" (4 tunes) is all from Scotland, collected by Greig. Group B has only one item, from Kinloch, so it may be a fluke. Group "A" has two tunes of unclear provenance.

So it's an interesting question which is the oldest tune. D is most widespread but is late. C is also later than A or B but looks like the most unified. A and B are poorly attested.

Just based on sources, I would guess "C" as most likely to be the earliest tune, but I can't hear it in my head just from looking at staff notation, so I can't tell you if it's any good.