Help identify this Omega ref

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Hi! I'm considering purchasing this watch. The case appears to be 14k gold-filled. The seller doesn't have the tool to open the caseback. Here are some photos. Thank you in advance.

 
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385
American market L6300, mid 1960s.
I'm sorry to bother you again but how do you know it is the one? I can't find anything on the internet about this model but a low quality photo on eBay. Thank you!