It was republished a few years ago. (I still have the original copy, the over-sized jammie, that I got when I was seven).

Here's an interview with Adams at Comic Book Artist Magazine:

ARLEN SCHUMER: Let's start with the cover: Originally, this project at DC Comics was going to be drawn by Joe Kubert, and for whatever reason, the Muhammad Ali people weren't happy with the likenesses, and somehow the idea came up, "Maybe we can get Neal to work on it."

NEAL ADAMS: Clearly, DC was having a problem with likenesses, and Ali's people weren't happy, so they had me take a try. They were happy with my likenesses, and basically, that was the turning point, and the reason I got the project.

When I saw Joe's original cover (he hadn't done detail to the background) with the two figures, I thought, "Gee, you know, no matter what I do, I don't think I'm going to come up with a better layout than Joe." So I essentially took his layout, and just put my own drawing into it, and if somebody recognizes the pose of, say, Superman as not being a typical Neal Adams pose, it's a Joe Kubert pose, adapted to my style.

ARLEN: I remember looking at this at the time, thinking, "This cover doesn't quite look like Neal."

NEAL: I wanted to keep Joe's name attached to it, and by using his layout, I paid homage to it. Because this is a classic Kubert layout: The one foot up, and the shoulder. The big question that entered my mind was, I knew it would have a wraparound cover, so how do I then make it an event? And I thought, "Why don't I put famous people on the cover watching the match?"

If you count them, I think there's something like 170 different likenesses there. For a cover, that's a lot of drawings. You don't really do that. But I guess I was caught up in it, in that, for instance, I had just met Kurt Vonnegut and I thought, "Gee, Vonnegut would be at this fight." Certainly Muhammad Ali's trainers would be there, and of course, if Superman were there, Lex Luthor would be there. [laughter] And Batman would be there... well, by the time I got that stuff going, we got carried away-it just turned into this ball of string that I just couldn't unravel. And it got to the point where I was saying, "If there's a circle there, I ought to put a person there... where do I stop?" [laughter] Where does it end? Well, it just never ended, we just kept on going and going and going.