The fronts are self explanitory, they are fronts. The rear is easier than you might think. Does your truck have an ABS sensor at the rear diff? If so, that is a 12 bolt, if not, it's a 10 bolt. People often refer to the fronts as 10 bolts as well, they are only smaller.
Hope that helps. All else fails, talk to one of the techs at Calmini and they will help you identify the diff.