I am unable to track the original source of your inscription. However, on Yahoo Answers
there is a ten year old thread which suggests the following...
"His name is fragrant and his rest is so peaceful, sleep and blessed are you."
This author "doethineb" also comments...
"I put "blessed are you" because "gwyn ei byd" is the beginning
of each verse of the Beatitudes in Matthew chapter 5. I think that there is a connection
with the Song of Solomon chapter 1 v 3: "Thine oils have a goodly fragrance; Thy name
is as oil poured forth". "