I have removed my cluster to fix the odometer that quit 3 years ago (one gear decided to slide on its shaft, disengaging itself from the other gear). The instructions are indeed in the service manual. Basically one needs to remove the cover under the steering column, the chrome trim in front of the cluster, the cover above the steering column, and few other things too (I remember loosening the steering column as well). Then one needs to disconnect everything on the back of the cluster, without breaking the little pins of the main board that connect to a rather big connector. Removing the ignition switch is also required as far as I recall. Then, once every retaining screw is removed, the speedo needs to be turned clockwise or counterclockwise so it can be extracted from under the dash (can't remember !), and pay attention not to scratch the face of the cluster on the rough edges of the dash. Your fingers might suffer a bit too. Got few scratches on mine, the edges on my dash were pretty rough.
I hope this helps ! Thank you very helpful