Hy modernbeat, there are at least a half dozen different possibilities for rear axles, depending on the trucks G.V.W., and its original usage. There are single speeds, two speeds, and double reduction rear ends possible in that year/size of truck. There are "corporation" rear axles (Salibury I think), Eatons, and Timkens. Some rear axles have the part number and the ring and pinion gear count stamped into the end of the pinion gear, just divide the small number into the big one to find the ratio, I hope that helps.
