Stars without number: What parts, if any, of the spell casting rules apply to Savage Sorcery?

Codex of the Black Sun includes an approach called Savage Sorcery (p. 91), along with rules for spell casting.

The use of level 1 Savage Sorcery is described as a "main action invocation." While "Invocation" is occasionally used throughout the Dark Sun Codex as a synonym for "Spell," it is also used to refer specifically to the vocal part of the spell casting.

So, the question is: What parts, if any, of the "Casting Spells" rules on page 21 apply to Savage Sorcery? Specifically:

Should it be declared at the beginning of the shift (and presumably it would be subject to failure due to injury)?

Can it be used in armor?