So most cards, when they grant additional actions, use the word "you may perform a free x action" such as in the case of IG-88C (When you perform a boost action, you may perform a free evade action). However, I noticed that cards that let you "acquire a target lock" don't use the same sentence structure, namely they leave off the word "action." I realize that the name of the action is "acquire a target lock" in the rulebook, so if something allows you to do so, such as Fire-Control System, does it follow the same rules as "performing a free x action" (can't perform while stressed, namely), even though it doesn't have the word "action" in the ability?

It does not. The word action is a keyword in X-Wing and if the word action does not appear, then it is not bound by the same restrictions as performing an action, nor does it trigger anything that would occur after performing an action.

I see, thank you very much!

You'll note similar lack-of-action token gains on cards like Guri, Attanni Mindlink, Rey (crew), and the pre-errata Tie/x7 title. You just get the token. This also gets around the once-per-turn restriction on actions, which is why Fire Control System is Quickdraw's favorite System.