When I removed my cluster to swap it out with one with a tach, I took the two screws (one on each side of the cluster) out and tilted it forward and disconnected the wire harness on top. At this point the only thing keeping you from removing the cluster is the shifter cable. There are two screws on the bottom of the cluster near the edges of the gear indicator area. If you take those two screws out you should be able to separate the gear indicator area and try to fix it. I do not know how to remove that entire shift cable because I did not have to remove it to replace cluster. I do have the entire gear shifter indicator assembly off of the one I bought on ebay if you need any parts. Also, how far is the gear position off? Mine are a tad off sometimes but it isn't that bad.
http://img369.imageshack.us/my.php?image=img8188mg1.jpg Pic of bottom showing the two screws to remove to gain access to the shift indicator.
http://img369.imageshack.us/my.php?image=img8189ub7.jpg This is the shift indicator. If it is really far off either the cable is stretched or the spring isn't springy anymore. I don't know, maybe someone else has a suggestion.