the auxillary spring pack was optional based on the GVW rating of the specific truck .... note in your manual that any nominal rating has a range of GVW's, the lower GVW is the "base" truck, higher ratings had different tires and/or wheel sizes and for some of the nominal ratings, the highest GVW has "aux rear springs" under 'equipment' ... commonly called 'helper springs' or 'overloads' in the day
Bill
