Drum lower ball joint is different from disk ball joint. I cant tell you just what the difference is though. It has been over forty years since I laid hands on a front drum brake Dart's ball joint. LOL Damn memory is slipping.
http://www.rockauto.com/
Look up: Dodge; Dart; 3.7; Suspension; ball joint. You will see several listings for both disk & drum brake equipped cars with photos. The difference may be as simple as attaching bolt size or spacing.
Rock auto has one of the easest parts house sites to navagate.