HP2, wouldn't the 4-link I described be considered an IRS? Let me know what the differnce is.
No, there is a key difference in the axle tubes. An IRS, Independent Rear Suspension, is similar to an IFS, Independent Front Suspension, in that each axle tube can move up and down independently of the other side, just like the front suspension moves. A live axle set up, which those four links are, has a single axle tube so when one side moves up or down, the pivot point is the wheel on the other side. This means when the wheels are in motion, they move in an arc whereas an IRS allows the wheels to move in a more vertical plane.