I would start with the question "why to you want to buy it?" This is not a particularly collectible piece, so getting all the parts to match may not make much difference in whether you got a good deal. The serial number on the movement and case# indicate those two pieces belong to each other. The case is dated to 1943ish and the movement is 1944ish. The crown does not look correct for the case, but can be ordered here if you wanted to replace it (
http://www.ofrei.com/page_147.html). The dial looks to be accurate, might have been redialed along the way at some point. The "A" in Omega is correct font for the era, and the logo is the older version too.