For instance the quote that Birch and Dupont attributed to Augustine about a new “French” emperor is very odd. The idea of the Franks was not in Augustine's time, and I can't find anything he said about an emperor from Gaul. Not saying that Augustine didn't say that, but if this is a well known prophecy, from a many who was famous for NOT having prophecy, then it would stand out. Unless it is another St. Augustine that is not as familiar.
The idea of a Greater France Emperor is hard to find in many older sources. Some make mention of a great King, but there are some who place him in what is now Germany, Britain, and a host of other places. In short, I would be very cautious unless you have a decent list of sources.
I lent out my copy of Trial, Tribulation, and Triumph (again) so I can’t look up whether Birch has the same reference to Augustine as DuPont at present.
There was also a St. Augustine of Kent, also known as Augustine of Canterbury, died 604, but a quick search revealed no “prophecy” associated with him.