control arm

The 73 Challenger disc brake SPINDLE is the same as the 73-76 A body disc brake setup. The upper control arm is different. The spindles & calipers are very desirable in a body brake conversions although you would have to use the 73-76 A body upper control arms. 73-74 E body spindles are also a direct bolt on to 66-70 B bodies for disc conversion.
This will help a lot:
DISC-O-TECH: Stop on a dime from Mopar Action and Rick Ehrenberg