The IRS springs were shorter. There were 6 different springs (for the various combinations of engine, Statesman, FE2 et cetera).
The live axle was fitted to wagons and utes, so there were 8 different springs for all the combinations.
The "country pack" springs with increased ride height were not available in IRS
Live axle has the rear axle combined with the diff housing in 1 solid unit. Looks like 1 solid bar from driver side to passenger side rear wheels, with the diff housing in the center.
Live axle does not have this solid bar look. Has a center diff, then the open axels leading dirctly to the wheels. The wheel has its own independant suspension setup much like the front wheel suspension setup on the front of the car.