Yes the hub size is bigger than the Mustang hub. I just did the Granada swap on my 67 Stang and had to use the rims off the Granada on the front. I am not sure what the actual size difference is, but Granada is bigger. Hope that helps.
the granada is somwhere around 1/8" bigger than the stock rotor snout. you can have the rotor snout machined down to fit the original wheels or you can have the original wheel centers machined to fit the granada snout if you so choose. if you're running aftermarket wheels you won't have to worry about it though.