I've never been there, but I got the information from a cunning combination of your description, Multimap and CARN.

CARN is a great resource for us Welsh based folk:

http://www.rcahmw.org.uk/data/

If you want more information, you could try contacting the NMRW.

http://www.rcahmw.org.uk/nmrw.shtml

Looking forward to seeing what you find if you go there.

K x