Upper stable loads which go between the extra spring back and frame will not require drilling since you already have the holes for the rubber pads. You will unbolt the existing rubber pads and then bolt in the new pads. Very easy to do.
The stable loads engage the spring sooner which is why they work. They take load off of the longer softer main spring pack and transfer the load to the shorter stiffer aux spring back.
If you are trying to reduce the sag, the stable loads will do that. However, if you are trying to reduce sway or body role, than you need a rear anti-sway bar like the Hellwig.