A very early 29-3 with an "N" prefix serial number. I have a 29-3 that was my very first new gun, first 29, and first 44 magnum and it has a three letter prefix. I think I bought it in 1989.
It was a 6" gun originally which I had cut to 5" and it currently has a recessed 29-2 cylinder in it. The gun has well over 30,000 rounds through it and when they put me in the oven the 29 will go with me.