early abody ball joint differences?

custom100 said

... but i do know that when i put a 73 and up disk brake kit on i had to change the lower control arms as well....

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I'm surprised by this.

I swapped my 69 dart without swapping the lower A arms..
I'm swapping a 67 dart as we speak, without swapping the lowers...

I've already bolted the lower BJ's from the 73 up into the arm without issue