Kev,
Have you tried looking forward/back from your entry to see any prominently named houses or farms, and then locating the area from it? I can't quite make out the name below your entry, 'Bryn_ _ _' something? If you can make it out (or another) let me know.
However, if you'd like to look at St.Davids Pit, go to old maps (
http://www.old-maps.co.uk)
then put in the co-ordinates 253800, 201400, this should take you right there. I don't believe there's much left to see there, I've driven past Bryn-bach farm and looked down the old tramway, but didn't have time for any more than that.
Regards,
Buckaroo