Hey GavinT - Without a lot of historical/maintenance documentation and a contact for the previous owner I'd be very suspicious of the odometer showing 61,000 miles. For a 78 model Porsche that would mean that either it has been driven only 2K miles/yr, the odometer has been replaced/inoperative or it has been dead in the water somewhere.
It looks nice in the photos but have a reputable 928 mechanic give it a thorough inspection before falling in love and any money changes hands. By the way - for 7.5K you can find LOTS of nice (newer) 928's for that kind of money in this economy.
Good Luck, Michael