Never measured Ol Shel's, but mine come in at 19" and 18" respectively (19 on sides, 18 on the nose and decklid). I've even posted pics of my large white meatballs in my gallery.
Seriously, I've never seen official meatball measurements in any of the books I've read (because many of them probably varied from car to car, race to race), but 19" has always looked right when comparing mine to all the vintage photos that are available.