Getting a good deal involves knowing what you want and what to look for to be sure that what you are looking at is what you think it is. Knowing what part numbers to check and what measurements to take helps to confirm that you are getting what you want or need. One week we picked up a Dana 44 for a TJ and an SM420 transmission. ID’ing the Dana 44 was easy—since we are Jeep nuts, we can spot one from 20 yards. The SM420 meant bringing a tape measure and checking numbers cast in the housing to be sure it was what we wanted.