Welcome to the club Datopower.

The dash (bit that holds the gauges) is pretty easy to get out. First off remove the windscreen wiper, headlight, heater controls, and choke knobs. The heater control knobs come off by undoing a small screw under the knob. Headlight knob will come off by pushing down on it and turning (i think) anticlockwise (might be the other way). Take off the collars behind the choke/headlight/windscreen wiper knobs. Remove your stereo front facia or whole unit.

There are two screws holding the dash in. They are located up under the dash, one behind the clock/tacho and one kind of inbetween the other two gauges. While you are working under the dash, remove the speedo cable (just unscrew it), and pull out the multi pinned plug from the gauge cluster. There might be a two other wires that need disconnecting but you will find that out when you try to pull the cluster out.

You might need to remove the plastic cover over the steering column to allow you more room to squeeze the cluster out. Once its out its pretty obvious how to take the gauges off. There was a wiring diagram floating around on here somewhere for installing the tacho, maybe someone can post a link to it?? if it is needed. Because i dont think you can just hook it up.