Normally, the trigger, trigger housing, and hammer are case hardened, not blue or nickel. I would doubt that S&W would have nickeled the whole gun, but never say never. If your gun has been sent back to the factory, it should have at least one or 2 marks that signify this. First, most have a star stamped near the serial number on the butt. Second, it you look under the left stock, you should find a 3 or 4 number stamp. Something like 1150 would mean the gun was returned to the factory on November 1950.
If the barrel address and serial number marks are in good shape, your gun would be a candidate for restoration. Personally, my preference would be to leave the the stocks, barrel, frame, and cylinder as is and simply have the nickel removed from the trigger, trigger guard, and hammer and re-case-harden the parts. The nickel shows age and that would actually give the gun more value than a fresh refinish in my opinion. Some character and signs of use are good things on a 140 year old gun.