It's a re-barrel with a later vintage (1950's) barrel. The best clue is that it has the barrel headed ejector rod and from the pictures, there is no cut out in the lug for the barrel head. Please see the picture in post number 2. That lug has the cut out.
Also the barrel did not receive its final contouring. The sharp ring at the rear of the barrel where the taper begins has not received its final contouring. A number of years ago, S&W did a giant parts sell-off and released a bunch of Outdoorsman barrels that were not finished. They had this sharp ring or transition. I would speculate that this is one of those barrels that was polished, blued and installed. It could be factory after the Outdoorsman went out of production using one of the unfinished barrels. I would lean towards factory because of the sight base corrosion.
By the way, S&W used hot carbona blueing when this gun was made (and up into the '70's) not blueing salts. That process involved packing the parts in bone charcoal and placing them in ovens. It also involved cyanide. One theory for the corrosion is that the surfaces of the sight base and the barrel were not cleaned properly to remove contaminants from machining. When the parts were heated the contaminants prevented the blueing from forming.