Why nail the "power metal" down to an isotope of gold with an atomic weight of 197? Because that's the only naturally occurring isotope of gold.
The "Emperor Carl" was, of course, Charles V, who also happened to be King of Spain, and therefore Pizarro's sovereign. I Germanicized his name, as I did the others—Francisco Pizarro becomes "Frank," et cetera—but this is perfectly legitimate. After all, the king's name in Latin, which was used in all state papers, was Carolus; the Spanish called him Carlos, and history books in English call him Charles. Either Karl or Carl is just as legitimate as Charles, certainly, and the same applies to the other names in the story.
As to the title "His Universal Majesty," that's exactly what he was called. It is usually translated as "His Catholic Majesty," but the word Catholic comes from the Greek katholikos, meaning "universal." And, further on in the story, when the term "Universal Assembly" is used, it is a direct translation of the Greek term, Ekklesia Katholikos, and is actually a better translation than "Catholic Church," since the English word church comes from the Greek kyriakon, meaning "the house of the Lord"—in other words, a church building, not the organization as a whole.
Toward the end of Chapter One, I wrote:
"Throughout the Empire, research laboratories worked tirelessly at the problem of transmuting commoner elements into Gold-197, but thus far none of the processes was commercially feasible."
I think you will admit that the alchemists never found a method of transmuting the elements—certainly none which was commercially feasible.
In Chapter Three, the statement that Pizarro left his home—Spain—with undermanned ships, and had to sneak off illegally before the King's inspectors checked up on him, is historically accurate. And who can argue with the statement that "there wasn't a scientist worthy of the name in the whole outfit"?
At the beginning of Chapter Four, you'll find:
"Due to atmospheric disturbances, the ship's landing was several hundred miles from the point the commander had originally picked ..." and "... the ship simply wasn't built for atmospheric navigation."
The adverse winds which drove Pizarro's ships off course were certainly "atmospheric disturbances," and I defy anyone to prove that a Sixteenth Century Spanish galleon was built for atmospheric navigation.