Hi Roger,
probably old news to your good self but I see the Gloster Non Conformists Archive has what I hope is Frank's Baptism, May 25 1878 Sewdley Chapel, parents James & Sarah.
Perhaps they also have more Records to interest you, I do hope so ?
eg they list six Drybrook Baptisms from 1906-1913, parents Frank & Nellie Griffiths ?? (these are all in FoD PRs too)
Whether this is same Frank I know not, looking at GlosBMD I see it's a popular Griffiths name in those days.

http://ww3.gloucestershire.gov.uk/genealogy/Results.aspx