I think I have found it on my 1841 map - Tor y cefn, roughly between Crwbin and Meinciau. Not sure if the farm is still there, but google gives several hits for properties in Tor-Cefn, Meinciau, Kidwelly. Tor-Cefn is shown on Old-Maps.co.uk. Same place as Tor y cefn in 1840.
Happy hunting!
Rhosgoch