Nothing on a stock Packard cares about polarity except the ammeter and to a lesser extent, the coil. If ammeter reads properly now, then someone switched in the past and changed it's connection as well. There is no compelling reason to change back unless you want to for the correctness of it.
If you need repairs to the radio in the future and have to replace the vibrator with one of the solid state replacements available today, that component will care so keep the change in mind if that happens to make sure you get the right one.
The R9 OD is a little more complicated than the R11 electrically but is not polarity sensitive and will work just fine. The biggest issue with the R9 electrically was shorts in the wiring or switch issues which might keep it engaged or cause it to engage inappropriately. If that happened when shifting to reverse or already in reverse, lock up and damage could occur. If your harness is a mess, check or repair it carefully.
There was a retrofit safety switch made available to be installed on cars with R9s.
packardinfo.com/xoops/html/downloads/SC/SC-VOL21NO15.pdf When car was shifted to reverse, the power to OD was completely disconnected so it was forced to disengage. It was a later change but your car may have the switch from the factory. If so, there will be 4 terminals on the backup light switch. 2 terminals next to plunger interrupt power to OD relay and back 2 are reverse light if you have that option, otherwise unused if no light. That might be a good switch to install if you have the original 2 terminal light only switch or nothing at all.
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