So both the 70-71 and 72-73 passenger car books are showing two mainshafts. PN 2892909 and 2892942. One is supposed to be 24 1/4 in. and the other is 26 23/64 in. (gotta love American measurements) Is it that one is 18 and the other 23 spline?? Why the difference in length?? And is there a difference in the yoke side spline count?? Thx, Bob