It is a sad quirk of history that the 351C was introduced right at a time when all of it's beneficial design features had to be curtailed due to legislative reasons.
It was the right thing at the wrong time.
If it had been able to hang on until the modern era of electronic control, fuel injection and engine management as did the smallblock Chev and smallblock Ford, all of it's difficult pollution control issues could have been eliminated without the detrimental effects on it's performance.
It could have taken it's rightful place as a "super engine" and been in far more widespread use.
The pre-historic pollution control devices and procedures of the seventies were responsible for the view that it was not viable to continue with it.
It hung on in Australia because pollution control legislation was not as strict as the US at the time and Ford Australia had discontinued smallblock production and put everything into retooling for the 351C.
The Australian market is small and Ford Australia, after such intensive investment, could not afford to go backwards so they were going with the 351C come hell or high water. So it lasted on for another ten years or so.
Some silly view in the eighties that nobody wanted to buy a car with a V8 led to it's demise in Aus.