Here is something interesting.
Assuming that the WM Lloyd mentioned is the one you are after (or even not so you can eliminate him).........
In a 1950 phone book there is this:
Lloyd, Rev W M, 18 Shelone Ter.
Tel: Briton Ferry 2127
Now...
Searching for him at Shelone Terrace brings up this
http://www.swansea.gov.uk/index.cfm?articleid=28558Which lists a paper in their archive
Certificates appointing an Authorised Person to register marriages, 1899-1953
<CB/NPT R 164> William Morgan Lloyd of 18 Shelone Terrace, Briton Ferry; Bethesda, Church Street, Briton Ferry; Congregationalists; 18 Nov 1930
[1 paper]
So... it looks like this is possibly the WM Lloyd referred to by Mrs T (Authorised 1930 and poss still living in Briton Ferry post WW2 in 1950)...although we do not know his age so cannot be sure.
Where did you get Morgan from? If it was from this reference it doesn't help. But if it came from somewhere else than that woud be useful corroboration.
There are some later phone book entries for a Rev WM Lloyd but not in Briton Ferry.
These may or may not be the same man and go on until at least 1963 so he would be really old (might be worth checking for deaths in Llandeilo to see if there is a death and what age it was).
In a 1953 phone book there is a Lloyd, Rev W. M. living at Morfa Gwyn
Phone: Aberporth 301
(Aberporth is in Cerdigion which is not near Cardiff or Briton Ferry so it may be a different man)
In 1959- 1963
Lloyd, Rev W.M. at 19 Diana Road,
Tel: Llandeilo 3214
(Llandeilo is Carmarthenshire)
Milly