This is a current ebay auction. The bottom and top perf rows look unevenly spaced to me, especially the bottom (5th perf from left, in particular, looks out of place). So maybe this is a modified #542 (10x11) to make the more expensive #545?
Despite the bad image, it appears to be a wide rotary press stamp. There is no way to alter another stamp like a 538 and end up with adequate side margins. The side margins are so wide that it is also possible that the stamp is a flat plate stamp distorted enough in the photograph to "pass" as a rotary press stamp. The perf 11 coil waste stamps were notorious for poorly aligned horizontal perforations. It is possible that sheets cut from the rotary press roll fragment were curled enough to cause problems with feeding them through flat plate perforators.
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