I know some would not agree and I don't want to start a flame war, but if it was mine and was passed down from my grandfather, in that condition I would send it to S&W for a re-finish.
I'm not recommending the OP do so, I am simply saying that having that old heirloom in a nice finish from the factory would enhance it's value to me. The preservation of old guns in original condition is overdone , in my opinion, when they have obviously degenerated to a condition where they are only for looking at and not much use for shooting and enjoyment; especially specimens that were made in plentiful numbers and can still be found in abundance. I can see not touching one that has some unique properties and was made only in small numbers with few surviving, but that's not what we're talking about.
I was tempted not long ago by an older S&W in 32-30 that was in 90% condition in original nickel. Sadly, I have just so many pennies to alot to the hobby and other wants/desires took precedence. But that's why I like these threads; they're educational, enjoyable, and very gratifying for me to see folks keeping family guns in the family.