info to convert a body drum to b body disc

am trying to upgrade my brakes on my 72 dart from drum 4" to disc 4 1/2 pattern,pulled the complete spindle assy off of a 76 coronet to install on my dart,i have a 73 newer upper a frame with large ball joint,however the lower ball joint is part of the lower control arm steering arm(don't know what it is called)this is different on the donor spindle it appears to be separate from the arm and instead installs up from the bottom of the lower control arm into the the steering arm thus it won't mount up,also the bolt centers are larger on the b body steering arm,can anyone tell me how to install these brakes,was told a easy switch,doesn't look it to me,you can email or better call 903-429-3093 i would appreciate any help....al

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