I haven't taken my AC out of my WRX, but the AC in my Miata weighs ~35 lb if that's any help.
Make sure you use lightweight (probably Subaru OEM unless you have tons of cash to burn) wheels as well as some lightweight tires.
Lift up all carpet aand remove the all sound deadining padding, then reinstall carpet so as not to look.....you know...
Some Miata people are obsessed with "adding lightness." There are some 1800 lb Miatas around.