Look again at the Reynolds 531 sticker and see if it mentions if it is double butted. If it does then Falcon frames of this level sell for about $250 on eBay. If it just says 531 Frame Tubing then it is seamless but not double butted and probably worth $100 as a frame. Plain gauge seamless 531 tubing rides nice and is a great candidate as the basis of a great bike. Double butted was found on their very nice high end bikes.

You wouldn't have a difficult time building that bike up with period correct components as Ernie Clements was one of the earliest adopters of Japanese components in the early 70's. You can build the bike up with any combination of Suntour and Shimano components including bar end shifters and still be duplicating an OEM setup. Nice thing about starting out with a nearly complete bike is you can get it on the road for little money to ride it long enough to find out what you really need to replace and you can leave alone things that feel fine.

The nicest aspect of your frame is that beautiful headbadge. Today the only bike brand I know of that still puts enamaled metal headbadges on all their bikes is Rivendell. Nice article in the most recent Rivendell Reader on how headbadges are made.