I've only heard this from one group and that was some 30 years ago. Other people may know more about it

Under this stone
Lies Gabriel John
Till the Year of Our Lord
Ten Thousand and one
Cover his head with turf or stone
'Tis all one, 'Tis all one

Pray for the soul
Of sweet gentle John
If you will, you may
Our let it alone
'Tis all one, 'Tis all one