Traditionally, catboats were heavily ballasted with either internal ballast or else a cast lead keel through which the centerboard was lowered. This gave them some degree of stability at low to moderate heel angles. While some Catboats used steel plate centerboards in most cases the centerboards themselves were just ballasted enough to sink when lowered and added nothing to the stability of the boat.
You can''t add a bulb to a hinged center board because you would be dragging the bulb sidewards through the water when the centerboard was partially raised.
Which now brings us gotten back to what I had originally been suggesting, in the "Best Hull Type" discussion, which is essentially a daggerboard with a bulb which would give you both the stability and sailing ability of a fin keel, with the shoal draft of a centerboarder. Daggerboards lift vertically rather than hinge so that the bulb always stays level. It is not all that difficult to design a daggerboard with a bulb that would work well. While a Tripp 26 or a Meleges 24r in no other way resembles what you are proposing to build, and they are far more sophisticated than you are proposing or even need, you might look at some pictures of the Tripp 26
or Melges 24
http://www.yachtworld.com/core/listing/pl_display_photo.jsp?slim=quick&boat_id=1314463&bo atname=24%27+Melges+Melges+24&photo_name=Picture+% 231&photo=1&url=
to see what this arrangement looks like.
The only problem with either a centerboard or a dagger board with a bulb is the space that they occupy within the cabin of the boat.