EURO market cars are built to provide room for the "billboard" plates they use in Europe.
Everything you now are stating is consistent with your car being a European Market build.
I actually looked at one to buy here that was a '72 model Euro build and to my memory, it DID NOT HAVE the bigger plate indent?
The difference in size is so apparent in person it is difficult not to notice it but memory being what it is, I could be mistaken?
I didn't think much of it then since I didn't buy it because it had rust EVERYWHERE.
The seller tried to convince me that "it is just cosmetic".
It did have metal ID plates riveted to the striker pillar posts with the name of the person that imported it and an EPA certification number which I had never seen before and found to be more cautionary then interesting actually.