As far as I know, King sights were always an aftermarket. I have a 38 M&P that was shipped in 1948 and delivered directly to King's in San Francisco. King's then put the Super Police Night Sight package on the pistol and sold it. I'm sure that more were done by the owners of the gun then sent directly to King's to do, but I am not sure.

As far as value goes, it's all in the eyes of the beholder. I really don't know how a King's ribbed sight would affect the value. If it was me, I would think it would bring a bit more money, but some people like their guns to be totally stock.