So I now have both the 27x40 DS Grindhouse (presumably the "real" thing) and the 26x39 DS Grindhouse (presumably the fake or commercial (?)).
It is certainly POSSIBLE that the 40 is fake, so I can't guarantee this authentication.
Overall, the 39 is VERY GOOD. If it were 27x40, it might very well pass as an original. The texture of both seems identical, smooth and slightly glossy. The image/photo quality appears very similar. I would guess that the 39 is produced from a very high resolution scan of the original.
But there are differences:
(1) The 40 inch is obviously larger than the 39 inch. Interesting that the "fake" just cuts off the edges - the image area is almost the same:
(2) The back of the 40 inch is lighter/whiter than the front but the 39 inch has mirror images:
(3) The 39 omits the "PRINTED IN USA" phrase:
(4) This poster recreates an old, beaten up, repaired/taped poster. You can clearly see one of the "taped" sections on the 40 towards the bottom center but the 39 totally lacks it:
(5) The small text on the 40 is sharper/more solid than then small text on the 39. However, the very small text on the 40 is also slightly fuzzy - not perfect like the old GAU logos:
(6) The 40 overall is yellower; the 39 is grayer/whiter. However, the colors are NOT dramatically different:
If you have one or both of these, please add your thoughts to this thread.