You forget the single line tank dates back to 1955 on Gale motors (and J/E accessory fuel pump kit). So your metal connector probably comes from that era. I just checked the 1955 Gale tank part list and the connector was 376156, same number as newer years. But you could buy all the little pieces of it separately in ’55.
I don’t think the o-ring ever was the same as a pressure tank. It was 303598
