Ball Joints

I'm replacing the upper and lower ball joints on my 72 GMC c-15 1/2. The new upper ball joint is held in by a 2-3'' snap ring, instead of the 4 bolts that replaces the rivets that I drill out with the old one. Should I use this one I have with the snap ring or take it back and try to find the one with the 4 bolts? Oversized is when the old ball joint makes a bigger groove and a larger width ball joint needs to go in to take up the worn out space, correct? Because they asked me if I needed oversized and I said no...THanks for the help.....