Someone just informed me that the 55/56 temperature sending unit is larger than the 57. The 55/56 is 3/8 NPT. I want to retain the 55 gauge and sending unit, but I will be using 57 "G" heads. It was suggested that the 57 sending unit bushing be drilled and tapped for the 55 sending unit. However, Concours sells the 3/8 NPT bushing. Is the OD of the 55/56 bushing the same as the 57? I would just as soon remove the 57 bushing and install the 55/56.