Chris here…
That’s amazing, Matt, what a brilliant piece to own! 
I was going to ask my “comics guru” Tim Perkins about this piece and what it is, but I’ve actually found a brilliant webpage that sheds some light on what this is: http://www.answers.com/topic/comic-book
To quote from the article itself:
Printing
[ul]
[li]The individual pages are arranged so they will appear in the proper order when the comic book is assembled. Usually, two or more pages are printed on each side of a single sheet of paper. For example, page 2 might be printed on the left half of a sheet and page 23 would be printed on the right half. On the other side of the sheet, page 24 would be printed on the left and page I would be printed on the right. On the next sheet, pages 4 and 21 would be printed on one side, and 22 and 3 would be printed on the other. And so on. When the sheets of paper are stacked on top of each other and folded in the middle, the pages appear in the proper order. On some printing presses, as many as eight pages can be printed on each side of a large sheet, then cut and folded as required.[/li][li]The plastic films for the four colors on each page are used to produce four aluminum printing plates. A bright light is projected through each film and onto the plate, which is coated with a chemical that is sensitive to light. Where there are dots on the film, they block the light and the chemical remains on the plate. Where there are no dots, the light passes through the film and burns away the chemical. This process is repeated for all of the pages that appear on each side of a single sheet (see Step 14).[/li][li]The plate for the first color on the front side of the sheet is fastened around a circular drum in the printing press, and the plate for the back side is fastened around another drum below it. When the press is turned on, water flows over the rotating plates, while rollers with colored ink press against them. Where the chemical dots remain on the plates, the ink sticks; where the chemical has been burned away, the ink washes off and doesn’t stick. The sheets of paper are fed between the rotating plates, and the front and back (top and bottom) sides are printed at the same time.[/li][li]This process is repeated for each of the four colors. In some presses, a long roll of paper is fed between four sets of rollers, and all four colors are printed in a single pass through the press. The printed sheets or the roll of paper are then cut to the proper size, stacked, folded, and stapled or glued to form the finished comic book.[/ul][/li]So, Matt, it would appear that where this plate is curved, that’s how it was meant to be - or at least, something that happened during the printing process!
I shall definitely do an article in the Comic Section’s “Special Features” subsection about this if that would still be OK - probably not as part of this update, but hopefully as part of the next one!
EDIT: Although, thinking about my above statement - do you think it would be acceptable for me to quote large segments of the webpage I linked to above (perhaps in exchange for a link to it)? If so, with those photos you’ve taken, it would actually be a really easy page to add to an update…
Take care…