I have made a quick comparison of the grip plates against those of the first and second version pistols, and you can see below that the checkering on the mystery pistol grips is coarser than on the second version and the WR logo is slightly different to that on the first version, but even so they are professionally done and IMO almost certainly original to the pistol.
Given the very low serial number of the mystery pistol, this suggests (to me) that both the front sight and the grip plates are original, and the gun may have been an experimental pre-issue model. I can understand why the front sight was never commercialised, but not why the checkered vulcanite grip plates were downgraded to smooth horn, if only for a short period. Unless it was just a cost issue.
This is a good example of a pistol that should have been left as found and not subjected to excessive restoration.