The d20pfsrd presents variant rules for called shots here. The source information for this page claims they come from the core rules, but I can't find them in the Core Rulebook. What source can I find these rules in? Did I miss them in some Paizo book, were they carried over from 3.5e, or from somewhere else?
The rules presented above state that "A called shot is a single attack made as a full-round action." But the feats dealing with called shots say "Normal: You can make one called shot per round as a standard action." Which of these is true? Is a typical called shot a standard or full-round action?
The page that you linked has a copyright notice that reads "Section 15: Copyright Notice - Pathfinder Roleplaying Game Ultimate Combat". It looks like these rules are in Ultimate Combat, which is not part of the core rulebook.
This is a typo in the original printings that has been officially errata'd:
In the Called Shot Feats sidebar, in the Normal entry for both feats, change “standard action” to “full-round action”.