Hi Len, welcome to the forum and website.

I cannot find any mention of a plan within this forum's old posts, or the rest of the site itself.

Have you tried asking the Church ?
http://www.lydneyparish.org.uk/contacts.php

This site doesn't have a plan, but if it included the burials you're interested in, then the photos should help.
https://www.findagrave.com/cemetery/2429303/memorial-search?page=1#sr-197304026

I could be wrong, but thusfar I cannot find any mention of Lydney in the various cds sold by Glos FHS.
eg http://gfhs.org.uk/products-page/cddvd/monumental-inscription-2003-2/

??