Richard,
I have today (Thursday, 11 May) visited West Glamorgan Archives and have accessed a list of burials at Capel y Baybel there are
NO plot numbers shown for any grave. So your request to:
.. .. locate the grave of my great grandfather, Benjamin Thomas, who is buried at the cemetery. .. .. cannot be found via that avenue of endevour.
Having seen the state of the burial ground, I certainly, and I doubt if anyone else will be able to find the grave by searching the actual burial ground itself.
Having said that I have looked for both Benjamin & Joseph.
I have found three entries for different Joseph Thomas, the most likely one being: with an address of Gendros, Raven Hill; buried 30 AUG 1902; age 20; (apparently) on page 5 of the original Burial Record.
However, there are five Benjamin Thomas' listed but none of which I can comfortably sugest is 'Your' Benjamin, they are: 1954, age 82; 12 Dec 1903 No age; 1921, age 80; 1925, age 51; 1933, age 79.
I'm not overly sure what other assistance I can provide.
JohnG_Swansea.