Your sending unit in a '55 tank should be located like this
https://www.ebay.com/itm/1955-Ford-G...wAAOSwzThcAVRX The 55-56 tanks are used in 52-54 Fords at times because they are harder to come by and twice as expensive as the 55-56 tanks.
https://www.ebay.com/itm/Gas-tank-fo...IAAOSwXVNbWc5d Notice the difference in location of the senders.