To add on to what eshew said....
IMO the Z2 Atom 80 is a better fork than the SID you have, and if the bushings are still good, I would spend $80 on that before throwing much effort and/or money into the SID.
The one thing to be aware of is that the Atom 80 is a coil fork. For the most part that is a good thing. This was better than the air options from that time. In fact, the Z1 and Z2 coils were arguably the best forks of the late 90s (again, IMO). The one possible downside in this case would be if the spring in this one you are looking at is not the right stiffness. You may have problems finding a replacement coil spring. So make sure the spring rate works for you.