I just got a Neptune I bought from a lady who thought it was a 1947, she actually found it in a Junk yard! There are a few pieces missing, so I am trying to find the exact year so I can possibly find parts, and have a better idea on its year. Its a Model AA1 J318UU. (I’m not positive if the ‘J” is part of the serial number, it’s Before the “3” but really close to the crank)I’ve been told its a 1947, another gentleman that has been helping out on here says between 1954-1956, so its hard to know the year really. My Tank is more Oblong shaped and not squared like some of the 54’s and 56’s I’ve seen. Keep in mind I just got this yesterday so I am really trying to study up. I have a 41″ and that was easy to find it’s year haha! Here are some pictures, any suggestions are appreciated!