I would take the engine out, test it again on the bench and open it up again to see what's happening inside.
I had the same thing happening to me on a window motor. A spring of the carbon brush had broken off, a few months after the rebuild.
Luckily it was the window motor of the quarter...
Usually the wining noise of a wheel bearing starting to fail, wiil be noticeable at certain speeds. And in some cases gets louder when cornering.
When the sound is coming from your dif, I would assume it is noticeable at all speeds.
This one's for sale in Denmark (and it even has a fartpilot!):
https://klassikermarkedet.dk/annoncer/chrysler-oevrige-new-yorker/
And this one in Belgium:
https://www.autoscout24.be/nl/aanbod/-4f457d81-29ed-44ef-88b5-ac09fc80cac1
That has turned into a very desirable car; I'm loving everything about it! Would you care to share some "before" pictures, and pictures of the restoration process?