advise for suspension setup for 67 dart

There's been quite a few fast, street, and ralley Mopars based on stock suspension

heavier torsion bars, SWAY BARS and good shocks and tires, and pay attention to alignment. The concensous is you do NOT want to use factory alignment specs

In the rear, same thing. Heavier springs, good shocks, tires and SWAY BARS

Cars with offset rear leafs can NOT corner with stockers because of the leverage caused against the roll center of the suspension