The ohm range you are looking for is 73-10 but the thing to watch out for with Ford senders is the mounting method and that Ford had different capacity tanks. The mounting for the 51-6 Packard tank needs a flat plate and O ring under it rather than a plate held on with screws. Because of the different tanks, some of the arms on the Ford senders are shorter than is needed on a Packard. There is a Ford sender listed in the x-ref but another poster bought that one a few weeks ago and found he had to do some mods for it to read correctly. Not sure why or if the correct sender is the one listed. On any Ford sender you may still need to bend the arm to match the Packard shape.
Unless someone knows for sure which Ford item to buy, for less money than a Ford sender or a repro Packard sender will cost, you might consider a universal Ford-Chrysler sender providing you have a sender at all that you can use and modify the mounting plate so it can mount.