There isn't a lot more to say about your revolver; Everything points to it being an Argentine government order gun as I mentioned, contemporary to your relative's service.
I do think that the gun has been refurbished, perhaps at a government arsenal long ago; The cylinder may also be a replacement, or at least has been heavily polished on its rear face as no pitting is present, and no remnant of the serial number remains.
If you're comfortable with what you now know, there is nothing else that I can tell you. If you wish, you could obtain a letter for the gun with the factory's information on it (instructions are on this site).
Update: I did find a copy of an S&W letter by Mr. Jinks from 2006 regarding one of these Argentine revolvers; It states that such-and-such serial number in .44 Russian was shipped from S&W to Hartley & Graham on 1/10/1881. This particular gun, a lower SN than yours, was shipped with a 6.5" barrel, blued, and had checkered hard-rubber grips--not wood. It also says that the shipment including this gun was for 2002 pieces, and that the shipment guns had 'stamping,' but not what the stamping was for nor whom the order was manufactured.
As your gun does not appear to have the Argentine Army stamping, and has numbered wood grips, it is possible that yours was an individual order--or differed from the one mentioned in the letter, as these guns weren't necessarily all 'manufactured' for the order, as some may have been sourced from 'stock,' and modified to suit (by the addition of the sling swivel post-marking of the serial number, for example). Sadly, the markings may have been obliterated during the refinish, as the characters were not very deep.
No matter what, though, you have a 141-year-old survivor from your country's past, and it's remarkably well preserved for a gun that saw active service for years.
