just out of interest the 500 had 17x34,the 550 17x37 but retained the same overall final drive by the 550 having a taller primary reduction,the idea was to drive the transmission and clutch faster giving better selection plus a few other changes in the transmission,i once tried a 37 rear on a 500 and got two blocks then went straight home and swapped it back,and i live in a hill n dale area!