ball joint issues

i have a 68 dart with /6 and small 9" drum brakes. because of the expense of available disk conversion kits plus shipping to hawaii, i've decided to go with the scarebird setup, at least for now.
i recently read (mopar action, i think) that the lower ball joint to control arm stud was so small that they said they would'nt drive a car equipped with em over 20 mph for fear of them breaking. i have recently installed a full p-s-t urethane kit w/ new ball joints.
am i putting myself in danger sticking with the older size ball joints ??
anybody else have problems with these or even heard of a ball joint stud breaking ?? .. i sure haven't.
..thanks