B50 or B30. Mid-1970's-1980's are what my memory says include the years of production.
I'm hoping that is a reflection in the side by the neck. If that is controls for electronics then I have never seen them there as part of a factory install.
Split bridge makes it earlier in the years of production but I could not give a date when the split bridge was replaced by a single bridge.
It looks small on you which might be evidence for a B30.
They can be found. A cash offer of $2000 and in person pickup might shake some loose. $800-$1200 is a more realistic range if you are patient. You pretty much need the original case because I don't think there is anything else that fits. The B50 is slightly larger but I can't recall anyone complaining because they settled for a B30. Big concern is whether a specific instrument needs a neck reset now or in the future. That isn't especially known to be common but there is fear that it would be expensive, if needed.
Why do you want one? How/where would you use it?
My B50. I was in an internet discussion with folks who were bragging on their Marshall Stacks. I took the picture because I thought it was funny in context and ironic because if you are running a B50 through an amp then you are definitely doing something the hard way.