For location of graves at St Mary's Lydney, have a look at www.gfhs.org.uk/products.htm. For a fiver you get the memorial inscriptions. If my memory is right, I also got a CD and map of the grave locations from GFHS (Gloucestershire Family History Society) who are right next door to the county archives in Alvin Street, Gloucester. If I were you, I wouldn't go to the churchyard beforehand, as part of it has been designated a conservation area which is code for "You'll never find what you're looking for unless you hack your way in." I found out where my family's memorial was but couldn't get to read it until two relatives who still live in Lydney had put in a great deal of labour.