if its a "3rd gen truck axle" then you have IFS. what I'm guessing is maybe its the "3rd gen front axle" being the 3rd type of axle design under these trucks.
79 and 80 had no gusset under the housing.
81-83 had a short gusset under the center of the axle and the 84-85 (in the USA anyway) had the gusset go all the way across the bottom of the axle.
