My son, to whom the GT has now passed, has done a damned nice job of upgrading/repairing such things as the exhaust, throttle body, front and rear suspension, etc. His thoughts now turn to improving the speakers in the car. He's asked me to post this question looking for suggestions on brands and being a high-school senior with cost being a factor. I'm sorry but I don't have the opening dimensions but I'd imagine Crutchfield does. He wants to know if he's strictly limited to ready made solutions or do various drivers suggest themselves? Ideas so he can work on his own short-list?