Suspension, sway bars, wheel&tire upgrades, help!!!

Has anyone done much for chassi stiffening?? I am wondering because this 408 seems to be making the car very squirly. when you mash on the gas even in a straight line, you can see the passenger side front dive down from the torque. when you let off to shift and hammer back into it, it jerks side to side... Anyone any info??
i'm pretty sure it is still the stock 318 torsion bars and no sway bars. what would help this the best? or do I need torque boxes and inner fender tube braces? I am just trying to narrow down the cause; either torsion bars, sway bars or chassi?