from "HP mopar" magazine: the best one is one from a 75 to 79 cordoba/coronet behind a 360 & it had a 5 clutch drum & a better pump compared to earlier ones & to avoid a lockup unit but I thought the LU's came later??? here is a link for some more info & I would Google it also. http://mmerlinn.com/catalog/lil_sis_4/tf_9nr/tf9nr010.htm EDIT found a note: LU started in 1978/& it is 26 splines/smooth end on tip of input shaft as opposed to splined all the way