Interesting to see you post that in light of this recent post.
https://smith-wessonforum.com/142145444-post22.html
As with all historical objects, sometimes the artifact reveals things that even primary source documentation indicates different. While not apples to apples, a portion of the carbine collector community now prefers 'uncorrected' examples. (It's not apples to apples because every manufacturer subcontracted parts and not every transfer has been documented). I think you should do what you think is right based on the evidence and your own persepective.
The shipping invoice clearly shows Hump Back hammer with this serial number, so regardless of what transpired, if I can find a correct one , that would be a step in restoring to original. The collectors here have convinced me that this is an important feature to this pistol, so I've decided the best thing to do is find the correct hammer for it.