Get yourself the 1973 V8 and up A body spindles, brakes and A arm and lower control arm, rotor with the 4.5 inch bolt pattern hub, and bolt it in and go stop better
I did that to my 1971 Duster street and strip, it stopped fine in the 1/4 mile running 134.+ MPH weighing 3450 Lbs. with me in that car
I used all the parts from a 1974 318 Duster with those stock disc brakes
I think the 1973 6 cylinder cars still had the small 4.0 inch bolt pattern them, Mopar drop them, the 4.0 bolt pattern, in 1974 is what i was told on here about them in 2002 or so when I built that car
I did mount the brake caliper so it was mounted behind the spindle by reversing the spindles from the right side to the left and vise a versus, it aligned fine and stop great with that change That help move some of the weight back towards the rear of the car helping traction without being seen