OK so my mom has one of these green eggs from the 50s, she gave it to me. It does not seem to match any of the sizes on here. The grid in here is 16 1/4 inch, the opening is 17 inch accross. It would appear to be somewhere between a medium and a large. Does anyone know anything about the really old ones? Should I just order parts for the medium or what? The grid for the large won't fit and the grid for the medium is narely big enough to stay on the fire ring.