It sounds like you need to swap the complete crossmember in as an assy(no problem), it should bolt right in. if you get 71-72 balljoints, they will fit into the 68 arms, & let you use the 72 spindles. then use the steer linkage from the 72, & you should be set. you may find a diff in the steer stops on the older arms, but a little grind on the stops (on the spindles), should give back the turning radius. Good luck , & have fun.....
L