Doubt about small caps tracking for centuries and regnal numbers

I am designing a book for self-publishing. I want to know two things. The first is if the numbers of centuries in Latin need to be set in small caps with space between the letters. The second is if the number of the kings need to be set in small caps with space between letters. For example, in this phrase: “In the XVIII century, the King Carlos III, blablabla”. If I look in many books, they never use extra tracking for centuries and regnal numbers. Should I set the type with no extra space? Thanks in advance, Rafael.

I’m sure you can find examples of different conventions. I would set Roman numerals in ordinary capital letters. Maybe with a little extra space between. I think it would look strange to mix small caps and lowercase within a single name.

Thank you Matthew. I will set both the roman numerals and regnal numbers in ordinary caps with just a bit of space between.

As you say, it looks a bit weird to see the regnal numbers in small caps. Just check this screenshot from my Master´s degree thesis. “Enrique II” and specially “III Señor de Buitrago” look strange.