489G
·Forgot to mention that the crown does bear an Omega logo (the "Ω"), and that the front case glass is missing.
Those 'Speedmasters' come up for sale from the same seller quite often, they're fakes that go to some lengths to deceive buyers. Sorry you ended up with one, but you've done us a service actually looking into where the parts come from / the inside. Can you photograph your watch thoroughly and maybe create a thread here?