https://www.omegawatches.com/planet-omega/heritage/vintage-details/14543/
My understanding is that the "-20" refers to the 20th iteration of case reference 2505. Experts, correct me if I'm wrong.
1) Dial looks off. Leaning toward re-dial, but need better pictures. I'm not sure if the indexes ("markers and needles") are solid gold. The style of the "12" is called a "mirrored index" and is a common feature of 1940s Omega dials.
2) Don't know the part number. You can probably find vintage crowns on the open market (eBay, third party suppliers, etc), but Omega may produce a modern replacement crown.
3) Diameter is 38 mm excluding the crown.
Regards,
Brandon
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