If you want it cleaned and calibrated, try JDO http://www.jdo1.com/ – they did a great job on mine in the old Morris Minor.
Your speedo cable could simply require replacing but as the car is in bits, I would change it anyway.
The 5w bulbs in the head illuminate pretty much nothing so when I went to 12v I uprated them to 10 watt, still not 100%, but better than they were!
BTW I have a spare set of CTA Polypropylene (non rot) door cards for a big boot TA available. Somehow I ended up with 2 pairs so the spares are going cheap if anyone wants them.