My opinion is that it is one of the permutations of the Newport/Neptune/Gloucester 16 footers. Very solid little boats, out of production though since about 1988. The Gloucester would be the later...
Two manufacturers of this type of boats are:
Hake Yachts, 4550 SE Hampton Court, Stuart FL 34997 * (772) 287-3200
http://www.seawardyachts.com/
and
Northshore Shipyard, Chichester Harbour...
The largest "swing" keel "production" yacht (ie. keel pivots/rotates into hull) is probably the Northshore Southerly 54rs. They have only just started construction, so if this does not count, then...