74 dart drum sbp to lbp disk

Hey Guys got a question...

I go and get the complete disc brake set up off of a 88 Fifth Avenue...but when I get every thing off of the 72 Dart I have a major concern. I know I removed the knuckle arm off of the lower control arm ball joint of the fifth avenue. but when i go to connect the knuckle arm to the lower control arm of the Dart i'm confused about where the ball joint is suppose to go.:banghead:
Are they even compatible?
Am I switching the lower control arms also?