Hi DJF I've just got back from the churchyard - no luck yet. But it was a grey afternoon & the 18th cent tombstones are badly eroded & covered with lichen. I might have more luck on a sunny day, perhaps. Quite a lot of the stones have been tidied up round the edge of the churchyard, so it might, anyway, not be possible to find the actual grave.
The Woodstock records went to Oxfordshire RO years ago. so it might be worth contacting them. I know there was a (tatty) plan of the old cemetary (different from the churchyard) and there might be one of the churchyard as well. Too dark to look in the church itself - I always feel it's a bit of a cheek to turn the lights on, but will try on a sunny day.
Maggott