Both of those trucks require a 0 to 30 ohm sending unit, Bill. If you are using a 12 volt system, you need a voltage reducer for the gauge itself. This sender only affects ohm readings, however and it should work fine for either 6 or 12 volt. When you get the gauge you will need to adjust it and on the one I bought I cut the height back to fit in the tank. Seems to me it was about 13 inches down to the horizontal baffle plate. Then you have to adjust the length of the swing rod. Typically you divide the fuel tank height by 2 and multiply that figure x 1.4 but there will be some data with the sending unit telling you how the maker designed it. On tanks like these (vertical tanks) you can hold the sender outside the tank at the height it will mount to see how the arm will swing...that is to say when it will bottom out and when it will top out.

~ Jon
1952 1/2 ton with 1959 235 | T5 with 3.07 rear end