I'm a newbie in watches. Have been offered this beautiful vintagy Omega Speedmaster. No card / box / receipt attached. Only thing I know about it is it's 39mm.

From my several weeks of knowledge in watches, I've not seen one that looks like it.

1) What exactly the model of this Speedmaster (except it's a Speedmaster)?
2) What year was it made?
3) Is it a collectible?
4) What's the value of a used one? (I'm offered what I consider a good price for around USD$1300).