Hello Len,

I purchased a copy of the CD - St Mary's Lydney Memorial Transcriptions back in 2010 which contained a churchyard plan. It showed all of the headstones, flat ledger tombstones & box table-top old tombstones - all numbered & arranged in blocks around the church. This CD was the work of a lot of people in the Forest of Dean branch of the Glos FHS.

I looked at the website of the Glos FHS (as Jeff suggested) & found that the CD I purchased then seems to be not available anymore. However, there is a CD entitled: St Mary Lydney - Monumental Inscriptions in stock priced at £5 on their website shop. It might also contain a churchyard map?
However, if your ancestors did not have a stone to mark their resting place, then their exact burial plot would of course not be shown on this map.

As the churchyard of St Mary's is so huge, I found the map & reference numbers of the graves invaluable in locating the tombstones of my Benfield & James ancestors.