Re: ball joints require whole control arm?
I'm not familiar with the Crossfire suspension, however, I was with the 68 Road Runner and a guy at a Firestone store told me about the same story. However, I was aware that on those years a small amount of "back and forth" was normal, having been down that road with my Dad's Dodge.
I'd suggest that you double check that story with someone more knowledgeable before spending bucks on something that may not be broken.