Hi Brelade, I felt sure there was only one Penallta Colliery in the area, I lived about a mile or so from Penallta in a place called Cascade.
If you google Bargoed Library and contact them by E-mail, and because you have full details of the incident I believe they will possibly be able to help you.
As far as I remember The Rhymney Valley & Merthyr Express was seperate from the South Wales Echo, the Echo covered Glamorgan and the South Wales Argus was for Monmouthshire, best wishes Rowley