I'm not aware of Martin Carthy having "reconstructed" the words to Scarborough Fair--it's a common song, and it's been well-known for a long time. There are certainly instances of his having done this ("Famous Flowers of Serving Man" for one), but I don't think it happened here.

FWIW, I took "Girl From the North Country" as Dylan's rewrite of Scarborough Fair, and "Boots of Spanish Leather" seems like a rewrite/response to "10,000 Miles" to me. The melodies have the same overall contour, but I think it's a stretch to say that "Boots" has a variant of the Scarborough Fair melody. I'm a fan, not a scholar, though, so my impressions carry little weight.