Brake conversion 73 duster

'73-6 6cyl. A-bodies could still have drum brakes. I wouldn't try messing around piecing a disc brake setup together. Safety being the main issue, but, the shear hassle trying to get everything to play well together is another reason. Get either a stock disc brake setup (my personal choice) or a kit from a known vendor. At least you currently have the large ball joint upper control arms, so, that won't be needed to be sourced.