Morning all, I too have signed up to run the Ridgeway this year. Crewed for my missus a few years ago when was injured and have been meaning to have a crack at it but other races have got in the way...not this year though 
I think these are the checkpoints jules:
CP1: 10.5 miles; Grid Reference 874071; Wellhead Farm on approach to Wendover where Ridgeway crosses Hale Road.
CP2: 16.8 miles; 823036; next to car park near Whiteleaf (just before Princes Risborough).
CP3: 24.5 miles; 741987; where Ridgeway crosses a minor road.
CP4: 31.7 miles; 683904; after field gate where Ridgeway crosses minor road to take road towards Swyncombe Church.
CP5: 43.7 miles; 598807; Goring Hall
CP6: 52.4 miles; 479840; Bury Down car park where Ridgeway crosses minor road.
CP7: 61.5 miles; 344851; Sparsholt Firs – car park
CP8: 69.4; 238818; 2145 to 0845; Charlbury Hill – junction of farm road and Ridgeway.
CP9: 79.9 miles; 157760; Near Barbury Castle - near car park and toilets.
Finish: 85miles; 101700; Avebury – The Social Centre.