Technical 56 F Truck fuel Gauge

I am after some info re the above fuel gauge-I understand they are 12V negative earth . I plan to run one in my 1940 standard instrument cluster-as they are a bolt in replacing the 6V positive earth unit- in my A Tudor and need to know the ohm rating so I can order a matching ohm fuel tank sender for the Duece tank I am running out back . Hope some one can help.