Whatever price you can find on the internet for the standard 1963 guitar, use as a starting point. Whether or not your a guitar player determines your next step.
IF YOU DO play guitar, check out a few key areas: are the pickups and hardware all still fully intact and functional? Is there any damage to the headstock or neck? Is the guitar still well set-up? Based on your own abilities, decide how well the guitar feels. If it deserves a great answer in all these questions, improve your starting idea a little bit more.
IF YOU DON'T play guitar, don't trust a dealer or anyone on determining the specific price of this beautiful guitar because, being a legitimate 1963 Guild, it's a valuable guitar and there's no telling what some people would say to an innocent person just to take it out of thier hands.
I'd say keep it in the family; maybe a son or nephew plays guitar? Wait until thier a mature enough age to maintain such a valuable instrument and keep it in the family. Vintage guitars are HOT on the market as the older they get, the more valuable they are, being that they are still in good condition, that is...
Whatever you do, try to make sure it stays in a hardcase in a nice temperate spot, and try to fiddle around on it every now and then to keep it playable.