Why do you state the mother-of pearl stocks are not original? The factory offered both MOP and ivory on this model, and the shape, thickness, and quality look like they should be factory. Unfortunately, both revolvers are low on the list of have-to-have collectible S&Ws.
They made a lot of Model 1, 3rd Issue revolvers and many survived - 131,163 made. They are no longer considered a firearm worth shooting by many, even though CCI makes a 22 CB Cap cartridge that works fine in this little revolver. I will venture a guess of $500+. It would have shipped 1872 or 1873.
The Model 1 1/2, 1st Issue is also a very nice revolver, but ammunition for this model has not been commercially available since the 1990s. There were only 26,300 made, but they never were in high demand by collectors. I have a special order full plate nickel gun in fine condition, but only value it at $400. These may go up to $600 depending on where they are auctioned and how many bidders want one. The serial number is in the 15,XXX range, not the 35,XXX range and would have left the factory most likely in 1866. Mine was 18,XXX and shipped in 1867.