Hello, I have one! I purchased it at an auction in FLA. Ref numbers 2857-2856 1-SC, 491 movement. 19 Jewels, 15890493 dates to 1956
I don't have good pictures. I will try to photograph. My has one difference, the dial is marked with Omega symbol, automatic, then Speedmaster.
On another post, someone said it was redialed. I not so sure. They also said the ref numbers weren't right. I was so glad to see your post because I do believe mine is real. The movement is beautiful. the back case is marked Seamaster at the top and Waterproof on the bottom. Any thoughts on the Speedmaster dial? Also, Omega has responded that they don't know about the ref numbers like you've mentioned in your post.
Paul
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