King-Seeley fuel gauges and senders are all interchangeable through 1955 (there are two generations of the internal sender design but that is not significant). 1956 is a standalone one year only gauge and sender design (terrible design) and is incompatible with anything else though they at first glance look identical to 1955 and pre. 1956 senders are all dual spade and always stamped '12v' (there are 1955ish 6v senders that have dual spades but have no stamp which differentiates them from 56)