I have 2 nickel 39-2's. One is 1974 with all nickel controls. The other is 1979 with blue controls. Neither has the "N" stamp on the frame. I'll have to respectfully disagree with RJ that the 39-2's with all nickel controls aren't factory! I think they went to blue controls later in production to save a few bucks.
edit: I'm kind of proud to have the blued 39-2 in the first pic and the nickel 39-2 in the second pic pictured in the SCSW 4th edition page 343 to represent this model.