Safest I could find:
from a comment in the southwalesargus.co.uk(they should know??) Gwalia Deserta XV

Bells of Rhymney
(poem by Idris Davies)

O what can you give me?
Say the sad bells of Rhymney.

Is there hope for the future?
Cry the brown bells of Merthyr.

Who made the mineowner?
Say the black bells of Rhondda.

And who robbed the miner?
Cry the grim bells of Blaina.

They will plunder willy-nilly,
Say the bells of Caerphilly.

They have fangs, they have teeth
Shout the loud bells of Neath.

To the south, things are sullen,
Say the pink bells of Brecon.

Even God is uneasy,
Say the moist bells of Swansea.

Put the vandals in court
Cry the bells of Newport.

All would be well if — if — if —
Say the green bells of Cardiff.

Why so worried, sisters, why
Sing the silver bells of Wye.

And that seems to match this YT of Idris Davies reciting it
www.youtube.com/watch?v=_PMXfpbFccg

One from the words in the book On the Air with Dylan Thomas: The Broadcasts

So the main difference from the poem seems to be missing out of
To the south, things are sullen,
Say the pink bells of Brecon.