If the will was proved at St. Davids there are the LDS Will Abstracts on
fiche which are at most Welsh record offices and, I believe, at the Society of
Genealogists in London. Each year has been indexed in several ways including
legatees. By looking at the 1645 fiche indexes you should be able to find
out in which will these legatees are referred to. You can then go ahead and
order the will from the NLW.
Bye for now