No, it will not work. That sender has a resistance of 70 E to 10 Full and would be correct for a 51-6 providing the float arm can be bent to fit the tank. The 48-50 sender mounts differently to the tank and those gauges used a sender with a heater operated bimetal contact with an on/off pulsing type operation and not straight resistance. Some Ford products of the era used the same type senders but the bimetal types are getting to be all but nonexistent.
Having said that, Tinman has done a lot of work on finding a modern straight resistance sender that can substitute in the 48-50 models and has a project blog for his 49 at the PAC site detailing some of his experiments. I do know the sender he used has a different ohm range than 10-70. He just recently finished his car and finally has it on the road. Has driven it to a couple of shows but don't know how many tanks of gas that has involved. From what he has posted and told me via PM it seems he may have found an answer but there is still a question on long term stability due to the gauge getting a constant signal vs on/off pulsing and how the constant signal makes the gauge respond.
I don't know if he is completely thru testing yet or if the ohm range of the sender that was mentioned in the blog might be the final version. The first experiments are in the blog but don't remember what page they start on. You might look thru his blog at the PAC site or send a private message to Tinman_70 for details. He also has a blog on this site but it is not as complete in detailing the sender work as the PAC entries.
The sender he used may not be usable as is on your tank without additional mounting pieces because his car has a different tank. What he used was another brand tank modified to fit the car but at least the sender ohm range would be a start. A modern universal sender in that range could probably be modified to fit the Packard tank or a better version needing less work and with ready made mounting adapters might be available at Classic.
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