I have found that you can use a 1940's and 1950's Ford or Mercury 6V gas tank sending unit to replace the OEM 1940 Ford gas tank sending unit. What you have to do is remove the top of the sending unit and adjust the little starwheel to make it match the OEM King Sealy dash gauge. Turning the star wheel CW makes the needle go to the FULL side and CW makes it register to the Empty side of the dash gauge. Perhaps you could do the same with a broken 1936 gas tank unit. You can use a 6V dry cell battery as a power source.