Your guess is as good as anyones. There are so many small details on the car that logically make little sense.
What I think is that geneally speaking, someone took over the overall engineering details on the car, like Ford Engineering, and rather then do actual engineering calculations on what the size of a component should be, modeled those decisions (copied an existing car) after another.
If you start closely comparing the 65 Mustang to the Pantera as far as dimensions like this, things become very suspicious.
The '65 Mustang front caliper is close enough to make me think that an engineer in Italy, just took a cross reference and picked out something that was "close enough" and available in Europe and went with that. That likely would get easy approval from both the Engineering department and the Accounting department.
If I was a prosecuting attorney, I could show the relationship of those two departments to the point of making you doubt they were not the same people?
That caliper does fit the scenario which both of us have just described. Take something that already exists and has been in production, and make it work, as inexpensively as you can.
Look at the spindle and the front bearing sizes. Those are all '65 Mustang dimensions and the bearings interchange.
I think the Legal Department sometimes was the Engineering Department and that one person was also the Accounting Department? Delara was long gone from these decisions.