Duster ball joint questions.

If you have a single piston caliper on your car, it's been converted over to a 73-76 A body disc brake system, or a B or E body disc brake system, which will require a upper control arm, with the large ball joint.
Or the small ball joint could be adapted with a sleeve that Doctor Diff sells to do that swap.
65 to 72 A body cars used Kelsey Hayes brakes that are 4 piston calipers.

I think you have some of us confused with whats on your car to give you an accurate answer.

Pictures sure do help.