I was going to recommend using Adywan's source. However, I don't think its entirely accurate, to me it seems like there are instances where he took some libertys, for instance in Luke and Obi Wan's first encounter the rocks are a bit too white. IMO, the GOUT is actually the most reliable source of color information available. The one good thing abut Adywan's cut is that he got the starfields and the laser blasts and engine glows right, because the SE totally desaturated them but the GOUT has jaggies, so Adywan's cut is probably the most reliable source for those elements.
Adding grain is an interesting idea, and it would certainly help smooth over the Laserdisk patches. You have to be really careful though, not only in amount, but because fake grain doesn't look the same as real grain, its not just a "mask" thats dropped over the image like digital grain, its actually part of the image itself and changes and fluxuates depending on the exposure and levels. Maybe I'm just a stickler for these types of photographic things. Anyway, there is grain as part of the SE image if you look at it, not much is needed to be added because those are from the original negatives with digitized comp-shots, a lot of the grain we are used to seeing is just dupe grain and would not be there if we were to go back to the original negatives. But its true that Lowry minimized some of the natural emulsion grain.