"This piece was done during the brief period Michael Golden was Art Director (or whatever the title was) at Marvel, and when he sent out a cover sketch it was virtually a finished drawing. One from which we were forbidden to stray too far. That's why, for instance, Storm doesn't look like my Storm. The whole drawing is more akin to me inking Michael." -- John Byrne
As the lineart above shows, the back cover was used as the front cover in later editions.