By the time you get just the heads cleaned up, magnafluxed, pin the studs, freshen the guides, cut the exhaust seats for hard inserts to survive unleaded fuel, grind seats and valves, install new springs, retainers, keepers and seals, you'll have way more invested in just the heads than a whole boneyard Gen III motor would cost.
Please be advised that the factory was able to pull 270 hp with two Carter WCFB carbs and 283 hp with Rochester fuel injection, so I don't think you're gonna step up to the plate and hit a home run like 300-350 hp, not with those heads. Put down the Hot Rod magazine and read everything you can on this Hotrodders.com site. Real people live here and tell real stories of their experiences.
Write down every number you can find on all the parts you have and list them for sale on Hemmings Motor News. There is surely some dude out there who needs them to complete his restoration.