The 70-71 linkage had bronze bushings, 72-74 has plastic bushings and required a shorter pin and larger diameter. The crank arm you're looking for for a three speed will be PN 2822289. 72-74 output shafts on the wiper motors also had the small output shaft, which is fine, because it will fit all the crank arms where the large output shaft won't fit the 518, 635, 918 crank arms. Heads exploding yet? Believe me, I know, I go through it every day