The car is in a foreign country, so who knows,
but, that being said you think we'd seen one like this before.
You can't base it being factory from looking at the installation, welds etc.
This is my 1969 Polara (CHP), the
factory added retractable shoulder belts (not the normal stowaway ones seen in most cars), to do this they welded a nut to a plate and welded it to the B-pillar, the original welds didn't look much different. We needed to replace the nut as it had a rusted broken bolt in it.
View attachment 1715540317
That being said, I do not know why the factory would deviate on your Dart and not use the roof mountings.
Alan
