On the later cars (78 and on) you don't need to try to drop the steering column, but if you have a tilt/tele, it helps to lower it a bit sometimes. The complete speedo/tach housing comes out if you release the small screws around the outside edge. (some hold the glass only by the way). The speedo cable has a spring clip affair - if can have a look underneath with a mirror maybe you'll get the idea, but basically, you push a small catch and the cable is released. To re-fit, it just pushes back and the clip "clicks" into place. It may help to remove the small panel at the base of the dash that the light override pull switch is attached to. Once you've done that you can ease the whole cluster out enough to get to the bulbs. If you are very brave you can pull out the multi connector and to get the cluster out. Beware, the "circuit board" is plastic and can get brittle over the years,so is easily damaged.