74/75 Ford L6000 with cat 3208

Questions on my Ford L6000 with a cat 3208, Looking for the temperature gauge sending unit, My gauge reads cold always , so i grounded gauge and it sweeps up , Ohm out sensor and its open .I went to my local napa ,they have no listing, Looking for a place to get this sensor.

Last question is what type of transmission fluid does this truck take? I think its and Allison unit , but not sure!

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74/75 Ford L6000 with cat 3208