That is the way to go. I've remarked on this method (with photos) several times before. General purpose spring compressors are general purpose and can be dangerous. If a spring compressor slips and cuts loose, you have a lethal projectile launched in your garage. Springs under compression are dangerous to mess with. I think this is the safest way to work on them on the Firebird. A threaded rod through the center of the spring won't cut loose like a dislodged spring compressor can.

Here is my photo again.