Are The Ball Joints ( Upper & Lower ) The Same Part?

I ordered from detroit axle a set of lower control arm with ball joints ( both sides ) and the upper ball joints ( both sides) . Well after 2 shipments , 1st shipment had a lower control arm and a part labeled x-8142 and a part labeled K-8142. A total of 3 parts, I am thinking they just shipped one side not both. So I phoned and emailed and after a while 4 days I received another lower control arm and a part labeled x-8142. So I am still missing the other ball joint. I am thinking it is a K-8142. Upon inspection the x-8142 and the K-8142 seem to be the same. Are the ball joints for the upper and lower the same for a 1968 mustang fastback 289? HELP!!

Yes , as far as I can tell there is a difference between the two and locally it is quite a bit easier to get the lower control arm with the ball joint as a package than separate. I do not know why but it is that way here.