Reference number is 14390-2SC. Movement is 285. Serial number is in the 17,500,000 range (not obscuring, it is just hard to read on the picture). Does the dial looks original?
To me the dial looks like an old refinish, but I could be wrong. I am basing my thinking on the shape of the S in seamaster and the wonky OM in OMEGA. Looks almost done free hand. Besides that the case looks like it was polished to an extent that it lost the edges. I also think the sweep seconds hand is a replacement. I like the hands though.
My first thought was redial as a google image search for that reference brings up very different dials, but @WatchVaultNYC sold this http://www.watchvaultnyc.com/Omega-Seamaster-30-14390-61-SC_p_168.html Which is similar.
The Omega lettering can at times have strange differences. I thought my Omega Geneve that had a strange M in the Omega and was a redial and so did many others on the forum. Until they found many other examples on the net with the identical lettering to mine and most members changed there mind or had doubts and thought it could be original after all. Three renowned vintage watch dealers in London said it looked original, then my watchmaker who is a recognised member on the forum said it was original. From time to time Omega authorised other third parties to do the dials like Singer. They can be differences on the same or similar models over different time periods. Of course redials are also a possibility, an issue when you are dealing with items being 45 plus years old.
Agree with what @PatrickJ says, but Google search 14390, you get TOTALLY different dials. This is a guy trying to pass off a watch as a ranchero look alike. I think.
Has anyone ever seen those two-tone daggers before? My brain knows nothing but my gut isn't buying any of this. Look at the small E in Omega, ........no way! I'm so confident.... that I am probably wrong!