Looks real good to me too and I agree with the previous comment with regards to the "Z" stamped on the barrel most likely being a sideways "N" as well.

So you have an "N" (nickel) marked cylinder and barrel and a "B" (blue) marked lower left side grip frame. No later applied factory rework date codes, serial numbers match, and the barrel markings look centered up properly. I'd say, unless I'm way off base here, that it most likely left the factory that way.......minus the trigger shoe of course!

Thanks for the additional pics, as I was curious as to what to expect if I ever run across such a unicorn. (Doubtful, but sometimes you just get lucky.)