I had a 639 in that condition, too pretty to use/fire. Besides, I had an old no dash 39 to shoot. It became a safe queen, so I traded it off for a 3" 625-3 (one of my better trades I must say!).
One way to tell vintage is by the trigger guard. The first 639s had a rounded trigger guard, up till about 1984 I believe. After that, they all had the squared off trigger guards like the 2nd generation S&W autos with 4 digit model #s (eg: 6906, 4506, etc). Of course, posting the serial # will enable us to tell you the exact year of manufacture.