dont take my word for granted on this one but i think its the #1 tube that wont work with the -73 up kframe because of where the sway bar is atached. the #1 tubecenterline goes almost straight down about 2½" outside the cylinderhead and in under the k frame and i think that gap is closed up by the swaybar, hope someone else can confirm this, if noone can i can go and give you some measurement ofwhere that tube goes if that is of any help :)