aston martin db4 series iii will cost up to £ 350,000 to restore but could then be worth as much as £ 750,000 .
attractive prospect for many car enthusiasts by offering rare chance to restore virtually-untouched db4 .
1,100 db4 series iii cars made from 1958 to 1963 - and this one will be auctioned in buckinghamshire .
engine was stripped , fully rebuilt and new chassis fitted in 1983 - but it has hardly been touched since .