"Which ones are by disembowelment?"
Not so much death by disembowelment, but in "Six Dukes Wen't a-Fishing" (a ballad not included in Child), the corpse has his bowels removed as part of the preparation for burial.
In Lady Diamond, the Lover's heart is ripped out and served up to the lady in a goblet.
Child Owlet is ripped apart by horses - don't suppose that would have done his bowels any good!
Jim Carroll