I just replaced all my ball joints. And I upgraded to the 03+ Passenger side arm. The one piece. The are completely upgradable from the 2piece arm to the 1piece. My understanding is that some manufacturers stopped producing the two piece arms, so they give you the 03+ 1piece arms as a cross reference number for the 2piece.
K8708T : Driver Side
K8710T : Pass side(2piece)
K80068 : Pass side(03+ 1piece)
K8695T : Lower(both driver and passenger)
I don't know if you know who you're going to buy from, but I highly suggest RockAuto.com. The local auto parts stores wanted about $475 total for 2 Moog uppers and 2 Moog lowers. Rockauto was $300 shipped for the same items. Roughly $105 per arm w/ joint. Roughly $30 for the lowers.
'01 XLT disguised as a '03 Fx4 Level II
Big. Loud. Slow. Bright.