[Henchman99942]

I use GCA for everything equipment also. There are rules for attacks on shoulders, elbows, knees. GURPS 4th - Low-Tech - Instant Armor has it. And there are some rules for front vs back attacks, like against the skull. I think it's -7 from the Front, -5 from the Back. (as per tactical combat and facing)

I don't mind putting in the work to make a functioning rules adjustment, so long as the extra work is all contained at the front end, and it doesn't terribly increase the number crunching during play. One extra roll to determine what part of an arm was struck isn't going to bog down combat. The problem comes about when you go back and try to retro fit it into preexisting rules and stats. Like is groin independent or part of abdomen? Can it be struck with attacks from the Left, Right and Back? What does that do to calculating armor piece by piece if the front and back are different?