ok theres an easier way to do this:
jack up the rear and put it in neutral. paint a line on the yoke, and a point of referance on the housing. have someone slowly trun the tire one full rotation, and count how many times the driveshaft spins. i.e 3 3/4 -3.73 etc
to check ls, leave the rear jacked up and spin one wheel, getting faster and faster, if it has functioning ls the other wheel will begin to spin the same way