That piece in the final picture is one of the side gun plates from an Ork Kill Kroozer/Terror Ship. One mounts on each side, roughly amidships between the head and the engines, above the wings. If/when I ever build a Space Ork fleet again, it's all going to be scratch built, because it is terribly hard to believe that those metal models represent 10 hull points or a reasonable amount of firepower (let alone mekboy-approved quantities of gun barrels sticking out in all directions).