To answer your question, this is a highly modified Challenger with a lot of one off parts....(in this particular case, the rear suspension.) An original Challenger does have drums in the rear that are on the outside of the axle shafts, not on the inside as this one shows.
I should probably also say the conversion in the rear is to coil-overs as opposed to springs, so that's probably another reason there wasn't enough room for the calipers and rotors to fit in their original locations.