The 29-2 started production about 1961.
The "diamond insert grip" was deleted in 1968.
The "N" serial prefix started (from S333454) in 1969.
The 6.5" barrel was discontinued (for 6") in 1979.
The 29-3 started production about 1982.
With your serial number your revolver's production year could be narrowed to within two years. (You can PM it if you don't want to post it. You can also XX the last couple of digits.)
S&W's historian, Roy Jinks, will also send you a official factory letter, if you request one.