I think what you are really refering to a Canting Keel, when I think of the term swing keel I think of small trailor sailors and such , which have keels that are retracted by a cable of some sort and swing up into the keel trunk. These have been around forever.
The Canting Keels on these go fast boats are the ones you hear of falling off and causing problems, but I still knew what you ment.
Courtney is My Hero
If a man is to be obsessed by something, I suppose a boat is as good as anything, perhaps a bit better than most - E.B. White