Rule #1 with S&W is always going to be "anything is possible", but when we have a mystery with very few ways of digging deeper, we are usually best served by the path of least resistance. That means... what is most likely. I would say most likely is that someone had a 669 slide and put it on a 469 frame. Or, someone dura-coated or otherwise gun painted your slide.

As for the hammer, I agree that I THINK they only ever came with bobbed hammers, so again... most likely is that someone swapped it out for the hammer you have.

You could try and call S&W with the serial number and see what they tell you, but I doubt you'll get far. You could request a letter, but that would be an expensive way to find out maybe very little.

Furthermore, if the gun isn't really close to mint (and original box is a big help!) then regardless of it being odd... it's just not worth a heap on the open market. It certainly isn't worthless, I just don't think it's likely (at all!) that it is some kind of humdinger that would generate a huge, high dollar sale.

If it's fully functional and runs well, in my opinion, it's a $300 gun, give or take.