Re: 1974 johnson 6, still in original box.
Would surely be a great item for display in a marina shop or a museum, but:
Thirty eight years stored in an uncertain environment would probably make it a big, big project to get her running. Even if there is no corrosion in the cylinders, gearbox and crankcase virtually every piece of rubber, every gasket except the head gasket, both condensors and coils and the water pump might need replacement. The good news is that the rope in the recoil starter is probably okay.
I would therefore second pecheux's suggestion and offer about $200.