The stock sender for a 48-50 is the bimetal type and as such is not a true resistance unit. The sender has a heater inside which is in series with the gauge heater. The heaters bend a bimetal strip and in the sender, operates a contact. It is more of an on/off type operation with the cycle times determined by how hard the float arm pushes against the diaphragm and bimetal strip. The changing pressure either delays or hastens the contact operation and heater cooling. The contact on time determines how much time the gauge heater is on to move the needle.
Having said that, there is a poster at the PAC forum who has done some experimenting with a constant resistance unit. From last report he had found a universal sender that would work along with the necessary hardware to mount in the Packard tank opening. Don't believe he has posted any followup info to know if there have been any side effects with the gauge getting a constant voltage instead of the on/off cycling.
packardclub.org/forum/viewtopic.php?f=8&t=2302 If you don't want to try aftermarket or the constant resistance, Kanter Auto or Max Merritt will probably have the proper sending unit but it will most likely be expensive and require an exchange. If your old one has self destructed then without an exchange even more expensive. There were also two size tanks in the 22-23 series so two different senders. Most models had the 20 gallon tank, but if yours is the 17 make sure you get the correct unit for your tank.
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