what size wheel for my dart?

HI everyone. I have a 1970 dodge dart swinger. slant 6 it has the regular wheels with hubcaps. i want to upgrade to the rally wheels but not sure how to measure to make sure the wheels i get will fit. I know the wheels are 14 inch. im looking on ebay at a set that are 14x5.5. does anyone know the factory size drum that came from the factory. the car is all stock, any help would be appreciated. thanks