Replace the disc and caliper brackets and the hoses if they are not the same.Measure the disc diameter to be sure they same and check for bearing correctness,mrmopartech
Not sure about this but weren't the upper control arms different from 72 to 73 with the 73 and later having a larger ball joint and larger spindles. This is what I got into when converting from the 4" to 41/2" bolt pattern on my 72 demon. I guess if you already have the 41/2" bolt pattern it would mean they have already been changed. Just a thought.
just like jim said uca(73-76 has bigger one), spindle, caliper, caliper bracket, rotor, lower bj. for aftermarket kits, i like SSBC, their rotors come with either bolt pattern and 4 piston calipers, cast iron or aluminum.