I remember seeing people make pieces out of coat hangers. you put one end into the frame and measure to the center of the axle. then you do the same for the other side. you need to get the belt tension correct also. you can buy a gauge. i think with my sportster a common method was twisting the belt a certain amount. it's been a while. trying looking on google or youtube
i removed the wheel today set my torque wrench low and kept turning it up till the nut turned on the axle came lose at 110 ft/lbs its a 3/4 axle so 60-65 ft/lbs is right ? i guess harley tech over tighten it last time if 60-65 ft/lbs is right .