Easier, heat the coils with a torch when they are supporting the vehicle, just go slow and have some keep a measuring tape from the ground to the fender lip.
Please don't ever do this with a coil spring! It will ruin the spring and is very dangerous. You will end up with this:
If you want to lower the rear cheap and easy, cut the rear coils (at the top) about 1.5 coils, and don't heat them! Don't use anything that will get them hot, heat ruins springs. Use a sawzaw, cut off wheel, etc... and go slow, keep the springs cool.