There are a couple of fiberglass Kosters around, some apparently in very good shape, so I'm sure when I'm ready to make the purchase that the boat I want will come find me. Someone who actually designed and build these boats himself, working in the business since the 50's!
If this is the case, there is no reason I can see that it couldn't be made to drain overside via a couple of thru-hulls.
EDIT: Looking at the photos again, it seems that any water getting into the cockpit as it is now will go straight into the bilges via the cockpit lockers and the engine access hatch.

Traditional small wooden sailing boat in the pond of park Jardin du Luxembourg, Paris, France. Thanks Udo, but I'm probably a better candidate for a "plastic" boat than a wooden one, as much as I'd like one.
Aside from the fact that this presents an issue as far as seaworthiness , it is also a source of freshwater into the bilge. I would want to make sure that the cockpit drained into a designated sump with it's own float switch and bilge pump if the waterline will not allow you to convert the cockpit to a self-bailing one.

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