It looks like the original painting was actually modified after the fact by Kelly himself as mentioned in the Heritage sale of the painting:
Ken Kelly Eerie #29 Cover Painting Original Art (Warren, 1970). If this painting looks a bit different from the published cover, that is because the artist, master painter Ken Kelly, altered it after the fact. The barbarian with the wild hair is gone, painted over with a calmer (but more sinister looking) bald swordsman. Even the background was changed. The woman in the foreground seems to be the only part that remains unchanged. The reverse side of the canvas wrapped board bears notations showing that this is indeed the original published cover, it has just been altered.