84 Pontiac Firebird needing a coil-spring

Hi:

I have a 1984 Pontiac Firebird in awesome shape. Its a 2.8l V6 with 80,000 original miles and full paperwork from out of the factory. IT was stored for 15 years and I'm doing my best to keep up with the maintenance of it. Its been a learning experience indeed:) (my dad was a muscle car freak and when I was younger, I was a grease monkey.).

Anyways, noticed last weekend it was sagging a bit on the passenger rear and it looked like a coilspring sagging and I took it in to have it looked at. Yup, 600.00 fix and I decided to check around to see how much the coil was etc.

My questions are:

1. Is it any easy fix? I've changed alternators, starters, honed cylinders etc and I have full access to a shop to do it myself.I've maintained it all myself since I bought it and don't have a problem getting my hands a bit dirty?
2. Do I need a spring compression tool or can I just put the jacks under the frame and let the axles hang down to remove it? Does that make sense?
3. Any tips for doing it? (Other than using a whole bunch of WD40 and letting it soak before hand?)
4. If its only sagging a bit on one side, should I do both of them on the back?

Thanks in advance.

Ms. Wannabe Wrenches