I'd keep the parts too but for resale, there's always someone looking for bits for their restore project.
Might be able to fund your obsession on those sales.
Tanks vary from year to year, 650's from 79 to 81 are the Z model and are squarish after that they went for the chopper look (CL,CS, Custom etc) and the tanks fit competely differently.
I'd wait until you have the bike then work forwards, we can give you tons of advice on here once we see what you are working on so we need good pictures, take a camera.