I replaced my tank sending unit. The replacement unit is supposed to be mounted at the top of the tank in a hole that has to be cut in the top of the tank. Instead, I modified it to fit the original side mounting and I think I used the original float arm. Also, an MGB tank unit looks to have the same sliding coil as the original Lotus one. For this combo, just replace the MGB float arm with the existing Lotus float arm and assemble that to the Lotus mounting assembly. My Lotus is a 1968. Good luck, Bator