I have a beautiful Marlin 39-A with the heat treated metal for color around the loading port. The serial Number is B 3945 and I'm sure it's at least 60 plus years old. Any idea when it was built and how much it's worth. My Dad taught me how to shoot with this gun back in the early 60's. Would I reduce the value if I polished off some rust spots and sanded the wood stock to remove scratches?