I like the tune Welch/Welsh first recorded in Wesley's 1742 "..Tunes...commonly sung at the Foundery" that comes across to me as a folk-tune.

http://www1.cpdl.org/wiki/index.php/Welsh_%28Come_thou_long_expected_Jesus%29_%28Anonymous%29

The Hymn Tune Index says:

Probably based on a traditional Welsh carol or other popular tune.

http://hymntune.library.uiuc.edu/CitationName.asp?B2=Find+Citations&R1=no&R2=no&R3=close&box1=ON&box2=ON&box3=ON

I'd love to know what the original Welsh words were !