There is only a slight difference in the length, but the rule of thumb is coarse thread on the LCA side is 73 and up, fine thread is everything before 1973
There is no difference in effective length. The difference in the strut rods is due to the change in the design of the strut rod bushings from the single piece bushings to the split, 2 piece bushings. It doesn't matter what year strut rods you use as long as you keep them paired with the strut rods bushings for the model year of the strut rods. They can be used with any K.
